database cleanup

Reserve book

.github/workflows/master.yaml

@@ -35,4 +35,36 @@ jobs:
       - name: SonarCloud Scan
         run: mvn -B clean verify -Psonar,component-test -Dsonar.login=${{ secrets.SONAR_TOKEN }}
         env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+  artifact:
+    name: Publish - GitHub Packages
+    runs-on: ubuntu-18.04
+    needs: [test, sonar]
+
+    steps:
+      - uses: actions/checkout@v1
+      - name: Set up JDK 11
+        uses: actions/setup-java@v1
+        with:
+          java-version: 11.0.4
+      - name: Publish artifact on GitHub Packages
+        run: mvn -B clean deploy -DskipTests
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+  docker:
+    name: Publish - Docker Hub
+    runs-on: ubuntu-18.04
+    needs: [test, sonar]
+    env:
+      REPO: ${{ secrets.DOCKER_REPO }}
+
+    steps:
+      - uses: actions/checkout@v1
+      - name: Login to Docker Hub
+        run: docker login -u ${{ secrets.DOCKER_USER }} -p ${{ secrets.DOCKER_PASS }}
+      - name: Build Docker image
+        run: docker build -t $REPO:latest -t $REPO:${GITHUB_SHA::8} .
+      - name: Publish Docker image
+        run: docker push $REPO

.gitignore

@@ -31,3 +31,4 @@ build/
 
 ### VS Code ###
 .vscode/
+sendgrid.env

Dockerfile

@@ -0,0 +1,11 @@
+FROM maven:3.6.3-jdk-11-slim AS build
+RUN mkdir -p /workspace
+WORKDIR /workspace
+COPY pom.xml /workspace
+COPY src /workspace/src
+RUN mvn -B -f pom.xml clean package -DskipTests
+
+FROM openjdk:11-jdk-slim
+COPY --from=build /workspace/target/*.jar app.jar
+EXPOSE 8080
+ENTRYPOINT ["java","-jar","app.jar"]

README.md

@@ -5,7 +5,33 @@
 
 This is a small application that provides basic REST endpoints for managing library (add new book, reserve, borrow it, etc.). 
 
+The technology behind it: 
+* Java 11
+* Postgres
+* Spring Boot 
+
 ## Installing / Getting started
 
-Description in future
+#### Using `docker-compose`
+
+In the terminal run the following command:
+```console
+$ docker-compose up
+``` 
+
+#### Using Maven
+
+First make sure that you adjust the configuration file - `src/main/resources/application.yml` with connection details to your database.  
+
+Then, in the terminal run the following command:
+```console
+$ mvn clean package
+$ mvn spring-boot:run
+```
+
+#### Inside IntelliJ (with H2 or Postgres database)
+
+First configure how you run the `LibraryHexagonalApplication.java` by adding `--spring.profiles.active=h2` (for H2 database) or `--spring.profiles.active=postgres` (for Postgres database) as a **Program argument**.
+
+Then just run the `LibraryHexagonalApplication.java` class so it will use H2 database (you don't need to have postgres database up and running).
 

docker-compose.yml

@@ -0,0 +1,31 @@
+version: '3'
+
+services:
+  postgres:
+    image: "postgres:9.6-alpine"
+    container_name: postgres
+    volumes:
+      - postgres-data:/var/lib/postgresql/data
+    ports:
+      - 5432:5432
+    environment:
+      - POSTGRES_SERVER=postgres
+      - POSTGRES_DB=library
+      - POSTGRES_USER=library
+      - POSTGRES_PASSWORD=library
+
+  library:
+    build: .
+    container_name: library-app
+    ports:
+      - 8080:8080
+    environment:
+      - POSTGRES_SERVER=postgres
+      - POSTGRES_DB=library
+      - POSTGRES_USER=library
+      - POSTGRES_PASSWORD=library
+    depends_on:
+      - postgres
+
+volumes:
+  postgres-data:

pom.xml

@@ -50,6 +50,16 @@
 			<artifactId>gson</artifactId>
 			<version>2.8.6</version>
 		</dependency>
+		<dependency>
+			<groupId>com.fasterxml.jackson.module</groupId>
+			<artifactId>jackson-module-jaxb-annotations</artifactId>
+			<version>2.11.0</version>
+		</dependency>
+		<dependency>
+			<groupId>io.vavr</groupId>
+			<artifactId>vavr</artifactId>
+			<version>0.10.3</version>
+		</dependency>
 
 		<dependency>
 			<groupId>com.h2database</groupId>
@@ -57,6 +67,21 @@
 			<scope>runtime</scope>
 			<version>1.4.200</version>
 		</dependency>
+		<dependency>
+			<groupId>org.postgresql</groupId>
+			<artifactId>postgresql</artifactId>
+			<version>42.2.12</version>
+		</dependency>
+		<dependency>
+			<groupId>org.liquibase</groupId>
+			<artifactId>liquibase-core</artifactId>
+			<version>3.9.0</version>
+		</dependency>
+		<dependency>
+			<groupId>com.sendgrid</groupId>
+			<artifactId>sendgrid-java</artifactId>
+			<version>4.4.8</version>
+		</dependency>
 
 		<dependency>
 			<groupId>org.springdoc</groupId>
@@ -106,6 +131,10 @@
 				</executions>
 				<configuration>
 					<reportsDirectory>${surefire.and.failsafe.report.dir}</reportsDirectory>
+					<includes>
+						<include>**/*ITCase.java</include>
+						<include>**/*ComponentTest.java</include>
+					</includes>
 				</configuration>
 			</plugin>
 			<plugin>
@@ -232,4 +261,12 @@
 			</build>
 		</profile>
 	</profiles>
+
+	<distributionManagement>
+		<repository>
+			<id>github</id>
+			<name>Library REST application (hexagonal)</name>
+			<url>https://maven.pkg.github.com/wkrzywiec/library-hexagonal</url>
+		</repository>
+	</distributionManagement>
 </project>

src/component-test/java/io/wkrzywiec/hexagonal/library/DatabaseCleanup.java

@@ -0,0 +1,42 @@
+package io.wkrzywiec.hexagonal.library;
+
+import org.springframework.beans.factory.InitializingBean;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import javax.persistence.EntityManager;
+import javax.persistence.PersistenceContext;
+import javax.persistence.Table;
+import java.util.List;
+import java.util.stream.Collectors;
+
+//https://gist.github.com/JorgenRingen/a56837fc07e630c32280b8e3d14c2d24
+
+@Service
+public class DatabaseCleanup implements InitializingBean {
+
+    @PersistenceContext
+    private EntityManager entityManager;
+
+    private List<String> tableNames;
+
+    @Transactional
+    public void execute() {
+        entityManager.flush();
+        entityManager.createNativeQuery("SET REFERENTIAL_INTEGRITY FALSE").executeUpdate();
+
+        for (final String tableName : tableNames) {
+            entityManager.createNativeQuery("TRUNCATE TABLE " + tableName).executeUpdate();
+        }
+
+        entityManager.createNativeQuery("SET REFERENTIAL_INTEGRITY TRUE").executeUpdate();
+    }
+
+    @Override
+    public void afterPropertiesSet() throws Exception {
+        tableNames = entityManager.getMetamodel().getEntities().stream()
+                .filter(e -> e.getJavaType().getAnnotation(Table.class) != null)
+                .map(e -> e.getJavaType().getAnnotation(Table.class).name())
+                .collect(Collectors.toList());
+    }
+}

src/component-test/java/io/wkrzywiec/hexagonal/library/borrowing/MakeReservationComponentTest.java

@@ -0,0 +1,96 @@
+package io.wkrzywiec.hexagonal.library.borrowing;
+
+import io.wkrzywiec.hexagonal.library.DatabaseCleanup;
+import io.wkrzywiec.hexagonal.library.TestData;
+import io.wkrzywiec.hexagonal.library.borrowing.model.BookReservationCommand;
+import io.wkrzywiec.hexagonal.library.inventory.infrastructure.BookRepository;
+import io.wkrzywiec.hexagonal.library.inventory.model.Book;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.web.server.LocalServerPort;
+import org.springframework.jdbc.core.JdbcTemplate;
+
+import static io.restassured.RestAssured.given;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
+public class MakeReservationComponentTest {
+
+    @LocalServerPort
+    private int port;
+
+    @Autowired
+    private BookRepository bookRepository;
+
+    @Autowired
+    private JdbcTemplate jdbcTemplate;
+
+    @Autowired
+    private DatabaseCleanup databaseCleanup;
+
+
+    private String baseURL;
+
+    @BeforeEach
+    public void init() {
+        this.baseURL = "http://localhost:" + port;
+
+        Book book = bookRepository.save(TestData.homoDeusBook());
+        jdbcTemplate.update(
+                "INSERT INTO available (book_id) VALUES (?)",
+                book.getIdAsLong());
+
+        jdbcTemplate.update(
+                "INSERT INTO user (first_name, last_name, email) VALUES (?, ?, ?)",
+                "John",
+                "Doe",
+                "john.doe@test.com");
+    }
+
+    @AfterEach
+    public void after() {
+        databaseCleanup.execute();
+    }
+
+    @Test
+    @DisplayName("Reserve available book")
+    public void givenBookIsAvailable_thenMakeReservation_thenBookIsReserved() {
+        //given
+        Long homoDeusBookId = jdbcTemplate.queryForObject(
+                "SELECT id FROM book WHERE title = ?",
+                Long.class,
+                TestData.homoDeusBookTitle());
+
+        Long activeUserId = jdbcTemplate.queryForObject(
+                "SELECT id FROM user WHERE email = ?",
+                Long.class,
+                "john.doe@test.com");
+
+
+        BookReservationCommand reservationCommand =
+                BookReservationCommand.builder()
+                .bookId(homoDeusBookId )
+                .userId(activeUserId)
+                .build();
+
+        //when
+        given()
+                .contentType("application/json")
+                .body(reservationCommand)
+        .when()
+                .post( baseURL + "/reservations")
+                .prettyPeek()
+        .then();
+
+        Long reservationId = jdbcTemplate.queryForObject(
+                "SELECT id FROM reserved WHERE book_id = ?",
+                Long.class,
+                homoDeusBookId);
+
+        assertTrue(reservationId > 0);
+    }
+}

src/component-test/java/io/wkrzywiec/hexagonal/library/inventory/AddNewBookComponentTest.java

@@ -1,11 +1,11 @@
-package io.wkrzywiec.hexagonal.library.application;
+package io.wkrzywiec.hexagonal.library.inventory;
 
 import io.restassured.RestAssured;
 import io.restassured.response.ValidatableResponse;
+import io.wkrzywiec.hexagonal.library.DatabaseCleanup;
 import io.wkrzywiec.hexagonal.library.TestData;
-import io.wkrzywiec.hexagonal.library.domain.book.dto.BookDetailsDTO;
-import io.wkrzywiec.hexagonal.library.domain.book.dto.ExternalBookIdDTO;
-import io.wkrzywiec.hexagonal.library.infrastructure.repository.BookEntity;
+import io.wkrzywiec.hexagonal.library.inventory.model.AddNewBookCommand;
+import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
@@ -13,15 +13,14 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.boot.web.server.LocalServerPort;
 import org.springframework.http.HttpStatus;
-import org.springframework.jdbc.core.BeanPropertyRowMapper;
 import org.springframework.jdbc.core.JdbcTemplate;
 
 import static io.restassured.RestAssured.given;
 import static org.hamcrest.Matchers.greaterThan;
-import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 @SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
-public class AddNewBookTest {
+public class AddNewBookComponentTest {
 
     @LocalServerPort
     private int port;
@@ -29,6 +28,9 @@ public class AddNewBookTest {
     @Autowired
     private JdbcTemplate jdbc;
 
+    @Autowired
+    private DatabaseCleanup databaseCleanup;
+
     private String baseURL;
 
     @BeforeEach
@@ -37,6 +39,11 @@ public class AddNewBookTest {
         RestAssured.enableLoggingOfRequestAndResponseIfValidationFails();
     }
 
+    @AfterEach
+    public void after() {
+        databaseCleanup.execute();
+    }
+
     @Test
     @DisplayName("Search for a new book in Google Books")
     public void whenSearchForBook_thenGetList(){
@@ -55,29 +62,36 @@ public class AddNewBookTest {
     }
 
     @Test
-    @DisplayName("Add new book to a database")
-    public void givenGoogleBooId_whenAddNewBook_thenBookIsSaved(){
+    @DisplayName("Add new book to a database & make it available")
+    public void givenGoogleBooId_whenAddNewBook_thenBookIsSaved() {
         //given
-        BookDetailsDTO homoDeusBookDetails = TestData.homoDeusBookDetailsDTO();
-        ExternalBookIdDTO googleBookId =
-                ExternalBookIdDTO.builder()
-                        .value(homoDeusBookDetails.getBookExternalId())
+        AddNewBookCommand addNewBookCommand =
+                AddNewBookCommand.builder()
+                        .googleBookId(TestData.homoDeusBookGoogleId())
                         .build();
 
         //when
-        ValidatableResponse response =
-                given()
-                        .contentType("application/json")
-                        .body(googleBookId)
-                .when()
-                    .post( baseURL + "/books")
-                    .prettyPeek()
-                .then();
+        given()
+                .contentType("application/json")
+                .body(addNewBookCommand)
+        .when()
+                .post( baseURL + "/books")
+                .prettyPeek()
+        .then();
 
         //then
-        String homoDeusSql = "select * from book where book_external_id = '" + homoDeusBookDetails.getBookExternalId() + "'";
-        BookEntity savedBook = (BookEntity) jdbc.queryForObject(homoDeusSql, new BeanPropertyRowMapper(BookEntity.class));
-        assertEquals(homoDeusBookDetails.getTitle(), savedBook.getTitle());
-        assertEquals(homoDeusBookDetails.getTitle(), savedBook.getTitle());
+        Long savedBookId = jdbc.queryForObject(
+                "SELECT id FROM book WHERE book_external_id = ?",
+                Long.class,
+                TestData.homoDeusBookGoogleId());
+
+        assertTrue(savedBookId > 0);
+
+        Long availableBookId = jdbc.queryForObject(
+                "SELECT id FROM available WHERE book_id = ?",
+                Long.class,
+                savedBookId);
+
+        assertTrue(availableBookId > 0);
     }
 }

src/main/java/io/wkrzywiec/hexagonal/library/BorrowingDomainConfig.java

@@ -0,0 +1,23 @@
+package io.wkrzywiec.hexagonal.library;
+
+import io.wkrzywiec.hexagonal.library.borrowing.BorrowingFacade;
+import io.wkrzywiec.hexagonal.library.borrowing.infrastructure.BorrowingDatabaseAdapter;
+import io.wkrzywiec.hexagonal.library.borrowing.ports.incoming.MakeBookAvailable;
+import io.wkrzywiec.hexagonal.library.borrowing.ports.outgoing.BorrowingDatabase;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.jdbc.core.JdbcTemplate;
+
+@Configuration
+public class BorrowingDomainConfig {
+
+    @Bean
+    public BorrowingDatabase borrowingDatabase(JdbcTemplate jdbcTemplate) {
+        return new BorrowingDatabaseAdapter(jdbcTemplate);
+    }
+
+    @Bean
+    public MakeBookAvailable makeBookAvailable(BorrowingDatabase database) {
+        return new BorrowingFacade(database);
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/InventoryDomainConfig.java

@@ -0,0 +1,29 @@
+package io.wkrzywiec.hexagonal.library;
+
+import io.wkrzywiec.hexagonal.library.inventory.InventoryFacade;
+import io.wkrzywiec.hexagonal.library.inventory.infrastructure.BookRepository;
+import io.wkrzywiec.hexagonal.library.inventory.infrastructure.GoogleBooksAdapter;
+import io.wkrzywiec.hexagonal.library.inventory.infrastructure.InventoryDatabaseAdapter;
+import io.wkrzywiec.hexagonal.library.inventory.infrastructure.SpringInventoryEventPublisherAdapter;
+import io.wkrzywiec.hexagonal.library.inventory.ports.incoming.AddNewBook;
+import org.springframework.context.ApplicationEventPublisher;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.client.RestTemplate;
+
+@Configuration
+class InventoryDomainConfig {
+
+    @Bean
+    SpringInventoryEventPublisherAdapter springInventoryEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
+        return new SpringInventoryEventPublisherAdapter(applicationEventPublisher);
+    }
+
+    @Bean
+    AddNewBook addNewBook(BookRepository repository, RestTemplate restTemplate, ApplicationEventPublisher applicationEventPublisher){
+        return new InventoryFacade(
+                new InventoryDatabaseAdapter(repository),
+                new GoogleBooksAdapter(restTemplate),
+                springInventoryEventPublisher(applicationEventPublisher));
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/LibraryHexagonalConfig.java

@@ -0,0 +1,14 @@
+package io.wkrzywiec.hexagonal.library;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.client.RestTemplate;
+
+@Configuration
+public class LibraryHexagonalConfig {
+
+    @Bean
+    RestTemplate restTemplate(){
+        return new RestTemplate();
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/BorrowingFacade.java

@@ -0,0 +1,42 @@
+package io.wkrzywiec.hexagonal.library.borrowing;
+
+import io.wkrzywiec.hexagonal.library.borrowing.model.ActiveUser;
+import io.wkrzywiec.hexagonal.library.borrowing.model.MakeBookAvailableCommand;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ReservationDetails;
+import io.wkrzywiec.hexagonal.library.borrowing.model.exception.ActiveUserNotFoundException;
+import io.wkrzywiec.hexagonal.library.borrowing.model.AvailableBook;
+import io.wkrzywiec.hexagonal.library.borrowing.model.exception.AvailableBookNotFoundExeption;
+import io.wkrzywiec.hexagonal.library.borrowing.model.BookReservationCommand;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ReservedBook;
+import io.wkrzywiec.hexagonal.library.borrowing.ports.incoming.MakeBookAvailable;
+import io.wkrzywiec.hexagonal.library.borrowing.ports.incoming.ReserveBook;
+import io.wkrzywiec.hexagonal.library.borrowing.ports.outgoing.BorrowingDatabase;
+
+public class BorrowingFacade implements MakeBookAvailable, ReserveBook {
+
+    private BorrowingDatabase database;
+
+    public BorrowingFacade(BorrowingDatabase database) {
+        this.database = database;
+    }
+
+    @Override
+    public void handle(MakeBookAvailableCommand bookAvailableCommand) {
+        database.setBookAvailable(bookAvailableCommand.getBookId());
+    }
+
+    @Override
+    public Long handle(BookReservationCommand bookReservation) {
+        AvailableBook availableBook =
+                database.getAvailableBook(bookReservation.getBookId())
+                .orElseThrow(() -> new AvailableBookNotFoundExeption(bookReservation.getBookId()));
+
+        ActiveUser activeUser =
+                database.getActiveUser(bookReservation.getUserId())
+                .orElseThrow(() -> new ActiveUserNotFoundException(bookReservation.getUserId()));
+
+        ReservedBook reservedBook = activeUser.reserve(availableBook);
+        ReservationDetails reservationDetails = database.save(reservedBook);
+        return reservationDetails.getReservationId().getIdAsLong();
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/application/NewBookWasAddedEventHandler.java

@@ -0,0 +1,20 @@
+package io.wkrzywiec.hexagonal.library.borrowing.application;
+
+import io.wkrzywiec.hexagonal.library.borrowing.model.MakeBookAvailableCommand;
+import io.wkrzywiec.hexagonal.library.borrowing.ports.incoming.MakeBookAvailable;
+import io.wkrzywiec.hexagonal.library.inventory.model.NewBookWasAddedEvent;
+import lombok.RequiredArgsConstructor;
+import org.springframework.context.event.EventListener;
+import org.springframework.stereotype.Component;
+
+@RequiredArgsConstructor
+@Component
+public class NewBookWasAddedEventHandler {
+
+    private final MakeBookAvailable makeBookAvailable;
+
+    @EventListener
+    public void handle(NewBookWasAddedEvent event){
+        makeBookAvailable.handle(new MakeBookAvailableCommand(event.getBookIdAsLong()));
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/application/ReservationController.java

@@ -0,0 +1,25 @@
+package io.wkrzywiec.hexagonal.library.borrowing.application;
+
+import io.wkrzywiec.hexagonal.library.borrowing.model.BookReservationCommand;
+import io.wkrzywiec.hexagonal.library.borrowing.ports.incoming.ReserveBook;
+import lombok.RequiredArgsConstructor;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequestMapping("/reservations")
+@RequiredArgsConstructor
+public class ReservationController {
+
+    private final ReserveBook reserveBook;
+
+    @PostMapping("")
+    public ResponseEntity<String> makeReservation(@RequestBody BookReservationCommand reservationCommand){
+        Long reservationId = reserveBook.handle(reservationCommand);
+        return new ResponseEntity<>("Reservation has been made with an id " + reservationId, HttpStatus.CREATED);
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/infrastructure/BorrowingDatabaseAdapter.java

@@ -0,0 +1,82 @@
+package io.wkrzywiec.hexagonal.library.borrowing.infrastructure;
+
+import io.wkrzywiec.hexagonal.library.borrowing.model.ActiveUser;
+import io.wkrzywiec.hexagonal.library.borrowing.model.AvailableBook;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ReservationDetails;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ReservationId;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ReservedBook;
+import io.wkrzywiec.hexagonal.library.borrowing.ports.outgoing.BorrowingDatabase;
+import lombok.AllArgsConstructor;
+import org.springframework.dao.DataAccessException;
+import org.springframework.jdbc.core.JdbcTemplate;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+
+@AllArgsConstructor
+public class BorrowingDatabaseAdapter implements BorrowingDatabase {
+
+    private JdbcTemplate jdbcTemplate;
+
+    @Override
+    public void setBookAvailable(Long bookId) {
+        jdbcTemplate.update(
+                "INSERT INTO available (book_id) VALUES (?)",
+                bookId);
+    }
+
+    @Override
+    public Optional<AvailableBook> getAvailableBook(Long bookId) {
+        try {
+            return Optional.ofNullable(
+                    jdbcTemplate.queryForObject(
+                    "SELECT book_id FROM available WHERE book_id = ?",
+                    AvailableBook.class,
+                            bookId));
+        } catch (DataAccessException exception) {
+            return Optional.empty();
+        }
+    }
+
+    @Override
+    public Optional<ActiveUser> getActiveUser(Long userId) {
+        try {
+            jdbcTemplate.queryForObject(
+                            "SELECT id FROM public.user as u WHERE u.id = ?",
+                            Long.class,
+                            userId);
+        } catch (DataAccessException exception) {
+            return Optional.empty();
+        }
+
+        List<ReservedBook> reservedBooksByUser = getReservedBooksByUser(userId);
+        return Optional.of(new ActiveUser(userId, reservedBooksByUser));
+    }
+
+    private List<ReservedBook> getReservedBooksByUser(Long userId) {
+        try {
+            return jdbcTemplate.queryForList(
+                    "SELECT book_id FROM reserved WHERE reserved.user_id = ?",
+                    ReservedBook.class,
+                    userId
+            );
+        } catch (DataAccessException exception){
+            return new ArrayList<>();
+        }
+    }
+
+    @Override
+    public ReservationDetails save(ReservedBook reservedBook) {
+       jdbcTemplate.update(
+               "INSERT INTO reserved (book_id, user_id) VALUES (?, ?)",
+               reservedBook.getIdAsLong(),
+               reservedBook.getAssignedUserIdAsLong());
+
+       ReservationId reservationId = jdbcTemplate.queryForObject(
+               "SELECT id FROM reserved WHERE book_id = ?",
+               ReservationId.class,
+               reservedBook.getIdAsLong());
+       return new ReservationDetails(reservationId, reservedBook);
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/model/ActiveUser.java

@@ -0,0 +1,36 @@
+package io.wkrzywiec.hexagonal.library.borrowing.model;
+
+import io.wkrzywiec.hexagonal.library.borrowing.model.exception.TooManyBooksAssignedToUserException;
+import lombok.EqualsAndHashCode;
+
+import java.util.List;
+
+@EqualsAndHashCode
+public class ActiveUser {
+
+    private final Long id;
+    private final List<ReservedBook> reservedBooks;
+
+    public ActiveUser(Long id, List<ReservedBook> reservedBooks) {
+        this.id = id;
+        this.reservedBooks = reservedBooks;
+    }
+
+    public ReservedBook reserve(AvailableBook availableBook){
+        if (reservedBooks.size() < 3){
+            ReservedBook reservedBook = new ReservedBook(availableBook.getIdAsLong(), id);
+            reservedBooks.add(reservedBook);
+            return reservedBook;
+        } else {
+            throw new TooManyBooksAssignedToUserException(id);
+        }
+    }
+
+    public Long getIdAsLong(){
+        return id;
+    }
+
+    public List<ReservedBook> getReservedBookList(){
+        return reservedBooks;
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/model/AvailableBook.java

@@ -0,0 +1,18 @@
+package io.wkrzywiec.hexagonal.library.borrowing.model;
+
+import lombok.EqualsAndHashCode;
+
+@EqualsAndHashCode
+public class AvailableBook implements Book {
+
+    private final Long id;
+
+    public AvailableBook(Long id) {
+        this.id = id;
+    }
+
+    @Override
+    public Long getIdAsLong() {
+        return id;
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/model/Book.java

@@ -0,0 +1,5 @@
+package io.wkrzywiec.hexagonal.library.borrowing.model;
+
+interface Book {
+    Long getIdAsLong();
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/model/BookReservationCommand.java

@@ -0,0 +1,13 @@
+package io.wkrzywiec.hexagonal.library.borrowing.model;
+
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Getter;
+
+@AllArgsConstructor
+@Getter
+@Builder
+public class BookReservationCommand {
+    private Long bookId;
+    private Long userId;
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/model/MakeBookAvailableCommand.java

@@ -0,0 +1,14 @@
+package io.wkrzywiec.hexagonal.library.borrowing.model;
+
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+
+@AllArgsConstructor
+@Getter
+@Builder
+public class MakeBookAvailableCommand {
+    private Long bookId;
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/model/ReservationDetails.java

@@ -0,0 +1,17 @@
+package io.wkrzywiec.hexagonal.library.borrowing.model;
+
+import lombok.EqualsAndHashCode;
+import lombok.Getter;
+
+@Getter
+@EqualsAndHashCode
+public class ReservationDetails {
+
+    private final ReservationId reservationId;
+    private final ReservedBook reservedBook;
+
+    public ReservationDetails(ReservationId reservationId, ReservedBook reservedBook) {
+        this.reservationId = reservationId;
+        this.reservedBook = reservedBook;
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/model/ReservationId.java

@@ -0,0 +1,16 @@
+package io.wkrzywiec.hexagonal.library.borrowing.model;
+
+import lombok.EqualsAndHashCode;
+
+@EqualsAndHashCode
+public class ReservationId {
+    private final Long id;
+
+    public ReservationId(Long id) {
+        this.id = id;
+    }
+
+    public Long getIdAsLong(){
+        return id;
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/model/ReservedBook.java

@@ -0,0 +1,24 @@
+package io.wkrzywiec.hexagonal.library.borrowing.model;
+
+import lombok.EqualsAndHashCode;
+
+@EqualsAndHashCode
+public class ReservedBook implements Book {
+
+    private final Long bookId;
+    private final Long userId;
+
+    public ReservedBook(Long bookId, Long userId) {
+        this.bookId = bookId;
+        this.userId = userId;
+    }
+
+    @Override
+    public Long getIdAsLong() {
+        return bookId;
+    }
+
+    public Long getAssignedUserIdAsLong(){
+        return userId;
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/model/exception/ActiveUserNotFoundException.java

@@ -0,0 +1,10 @@
+package io.wkrzywiec.hexagonal.library.borrowing.model.exception;
+
+public class ActiveUserNotFoundException extends RuntimeException {
+    public ActiveUserNotFoundException(Long bookId){
+        super("There is no active user with an ID: " + bookId,
+                null,
+                false,
+                false);
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/model/exception/AvailableBookNotFoundExeption.java

@@ -0,0 +1,10 @@
+package io.wkrzywiec.hexagonal.library.borrowing.model.exception;
+
+public class AvailableBookNotFoundExeption extends RuntimeException {
+    public AvailableBookNotFoundExeption(Long bookId){
+        super("There is no available book with an ID: " + bookId,
+                null,
+                false,
+                false);
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/model/exception/TooManyBooksAssignedToUserException.java

@@ -0,0 +1,10 @@
+package io.wkrzywiec.hexagonal.library.borrowing.model.exception;
+
+public class TooManyBooksAssignedToUserException extends RuntimeException {
+    public TooManyBooksAssignedToUserException(Long userId){
+        super("You can't assign another book to user account: " + userId + ". Reason: Too many books already assigned.",
+                null,
+                false,
+                false);
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/ports/incoming/MakeBookAvailable.java

@@ -0,0 +1,7 @@
+package io.wkrzywiec.hexagonal.library.borrowing.ports.incoming;
+
+import io.wkrzywiec.hexagonal.library.borrowing.model.MakeBookAvailableCommand;
+
+public interface MakeBookAvailable {
+    void handle(MakeBookAvailableCommand bookAvailableCommand);
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/ports/incoming/ReserveBook.java

@@ -0,0 +1,7 @@
+package io.wkrzywiec.hexagonal.library.borrowing.ports.incoming;
+
+import io.wkrzywiec.hexagonal.library.borrowing.model.BookReservationCommand;
+
+public interface ReserveBook {
+    Long handle(BookReservationCommand bookReservation);
+}

src/main/java/io/wkrzywiec/hexagonal/library/borrowing/ports/outgoing/BorrowingDatabase.java

@@ -0,0 +1,15 @@
+package io.wkrzywiec.hexagonal.library.borrowing.ports.outgoing;
+
+import io.wkrzywiec.hexagonal.library.borrowing.model.ActiveUser;
+import io.wkrzywiec.hexagonal.library.borrowing.model.AvailableBook;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ReservationDetails;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ReservedBook;
+
+import java.util.Optional;
+
+public interface BorrowingDatabase {
+    void setBookAvailable(Long bookId);
+    Optional<AvailableBook> getAvailableBook(Long bookId);
+    Optional<ActiveUser> getActiveUser(Long userId);
+    ReservationDetails save(ReservedBook reservedBook);
+}

src/main/java/io/wkrzywiec/hexagonal/library/domain/book/BookFacade.java

@@ -1,24 +0,0 @@
-package io.wkrzywiec.hexagonal.library.domain.book;
-
-import io.wkrzywiec.hexagonal.library.domain.book.dto.BookDetailsDTO;
-import io.wkrzywiec.hexagonal.library.domain.book.dto.ExternalBookIdDTO;
-import io.wkrzywiec.hexagonal.library.domain.book.ports.incoming.AddNewBook;
-import io.wkrzywiec.hexagonal.library.domain.book.ports.incoming.GetBookDetails;
-import io.wkrzywiec.hexagonal.library.domain.book.ports.outgoing.BookDatabase;
-
-public class BookFacade implements AddNewBook {
-
-    private BookDatabase database;
-    private GetBookDetails getBookDetails;
-
-    public BookFacade(BookDatabase database, GetBookDetails getBookDetails) {
-        this.database = database;
-        this.getBookDetails = getBookDetails;
-    }
-
-    @Override
-    public void handle(ExternalBookIdDTO externalBookIdDTO){
-        BookDetailsDTO bookDetails = getBookDetails.handle(externalBookIdDTO.getValue());
-        database.save(bookDetails);
-    }
-}

src/main/java/io/wkrzywiec/hexagonal/library/domain/book/dto/BookDetailsDTO.java

@@ -1,24 +0,0 @@
-package io.wkrzywiec.hexagonal.library.domain.book.dto;
-
-import lombok.Builder;
-import lombok.EqualsAndHashCode;
-import lombok.Value;
-
-import java.util.List;
-
-@Value
-@Builder
-public class BookDetailsDTO {
-
-    private String bookExternalId;
-    private String isbn10;
-    private String isbn13;
-    private String title;
-    private List<String> authors;
-    private String publisher;
-    private String publishedDate;
-    private String description;
-    private int pages;
-    @EqualsAndHashCode.Exclude
-    private String imageLink;
-}

src/main/java/io/wkrzywiec/hexagonal/library/domain/book/ports/incoming/AddNewBook.java

@@ -1,7 +0,0 @@
-package io.wkrzywiec.hexagonal.library.domain.book.ports.incoming;
-
-import io.wkrzywiec.hexagonal.library.domain.book.dto.ExternalBookIdDTO;
-
-public interface AddNewBook {
-    void handle(ExternalBookIdDTO externalBookIdDTO);
-}

src/main/java/io/wkrzywiec/hexagonal/library/domain/book/ports/incoming/GetBookDetails.java

@@ -1,7 +0,0 @@
-package io.wkrzywiec.hexagonal.library.domain.book.ports.incoming;
-
-import io.wkrzywiec.hexagonal.library.domain.book.dto.BookDetailsDTO;
-
-public interface GetBookDetails {
-    BookDetailsDTO handle(String bookId);
-}

src/main/java/io/wkrzywiec/hexagonal/library/domain/book/ports/outgoing/BookDatabase.java

@@ -1,8 +0,0 @@
-package io.wkrzywiec.hexagonal.library.domain.book.ports.outgoing;
-
-import io.wkrzywiec.hexagonal.library.domain.book.dto.BookDetailsDTO;
-
-public interface BookDatabase {
-
-    void save(BookDetailsDTO newBookDTO);
-}

src/main/java/io/wkrzywiec/hexagonal/library/email/EmailContent.java

@@ -0,0 +1,4 @@
+package io.wkrzywiec.hexagonal.library.email;
+
+public class EmailContent {
+}

src/main/java/io/wkrzywiec/hexagonal/library/email/EmailCreator.java

@@ -0,0 +1,10 @@
+package io.wkrzywiec.hexagonal.library.email;
+
+class EmailCreator {
+
+//    EmailContent prepareEmailContent() {
+//        // email to
+//        // email from
+//        //
+//    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/email/EmailSender.java

@@ -0,0 +1,6 @@
+package io.wkrzywiec.hexagonal.library.email;
+
+
+public interface EmailSender {
+//    void sendReservationConfirmationEmail(ReservationDetails reservationDetails);
+}

src/main/java/io/wkrzywiec/hexagonal/library/email/SendGridEmailSender.java

@@ -0,0 +1,33 @@
+package io.wkrzywiec.hexagonal.library.email;
+
+//import io.wkrzywiec.hexagonal.library.borrowing.model.ReservationDetails;
+
+public class SendGridEmailSender implements EmailSender {
+
+//    @Override
+//    public void sendReservationConfirmationEmail(ReservationDetails reservationDetails) {
+        // email address - to
+        // repl9oservation id
+        // book title`
+
+//        Email from = new Email("test@example.com");
+//        String subject = "Sending with SendGrid is Fun";
+//        Email to = new Email("test@example.com");
+//        Content content = new Content("text/plain", "and easy to do anywhere, even with Java");
+//        Mail mail = new Mail(from, subject, to, content);
+//
+//        SendGrid sg = new SendGrid(System.getenv("SENDGRID_API_KEY"));
+//        Request request = new Request();
+//        try {
+//            request.setMethod(Method.POST);
+//            request.setEndpoint("mail/send");
+//            request.setBody(mail.build());
+//            Response response = sg.api(request);
+//            System.out.println(response.getStatusCode());
+//            System.out.println(response.getBody());
+//            System.out.println(response.getHeaders());
+//        } catch (IOException ex) {
+//
+//        }
+//    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/infrastructure/BookDomainConfig.java

@@ -1,36 +0,0 @@
-package io.wkrzywiec.hexagonal.library.infrastructure;
-
-import io.wkrzywiec.hexagonal.library.domain.book.BookFacade;
-import io.wkrzywiec.hexagonal.library.domain.book.ports.incoming.AddNewBook;
-import io.wkrzywiec.hexagonal.library.domain.book.ports.incoming.GetBookDetails;
-import io.wkrzywiec.hexagonal.library.domain.book.ports.outgoing.BookDatabase;
-import io.wkrzywiec.hexagonal.library.infrastructure.adapter.BookDatabaseAdapter;
-import io.wkrzywiec.hexagonal.library.infrastructure.adapter.GoogleBooksAdapter;
-import io.wkrzywiec.hexagonal.library.infrastructure.repository.PostgresBookRepository;
-import org.springframework.context.annotation.Bean;
-import org.springframework.context.annotation.Configuration;
-import org.springframework.web.client.RestTemplate;
-
-@Configuration
-public class BookDomainConfig {
-
-    @Bean
-    RestTemplate restTemplate(){
-        return new RestTemplate();
-    }
-
-    @Bean
-    BookDatabase bookRepository(PostgresBookRepository repository){
-        return new BookDatabaseAdapter(repository);
-    }
-
-    @Bean
-    GetBookDetails getBookDetails(RestTemplate restTemplate){
-        return new GoogleBooksAdapter(restTemplate);
-    }
-
-    @Bean
-    AddNewBook addNewBook(BookDatabase database, GetBookDetails getBookDetails){
-        return new BookFacade(database, getBookDetails);
-    }
-}

src/main/java/io/wkrzywiec/hexagonal/library/infrastructure/adapter/BookDatabaseAdapter.java

@@ -1,41 +0,0 @@
-package io.wkrzywiec.hexagonal.library.infrastructure.adapter;
-
-import io.wkrzywiec.hexagonal.library.domain.book.dto.BookDetailsDTO;
-import io.wkrzywiec.hexagonal.library.domain.book.ports.outgoing.BookDatabase;
-import io.wkrzywiec.hexagonal.library.infrastructure.repository.AuthorEntiy;
-import io.wkrzywiec.hexagonal.library.infrastructure.repository.BookEntity;
-import io.wkrzywiec.hexagonal.library.infrastructure.repository.PostgresBookRepository;
-import lombok.RequiredArgsConstructor;
-
-import java.util.List;
-import java.util.Set;
-import java.util.stream.Collectors;
-
-@RequiredArgsConstructor
-public class BookDatabaseAdapter implements BookDatabase {
-
-    private final PostgresBookRepository repository;
-
-    @Override
-    public void save(BookDetailsDTO bookDetailsDTO) {
-        BookEntity bookEntity = BookEntity.builder()
-                .bookExternalId(bookDetailsDTO.getBookExternalId())
-                .isbn10(bookDetailsDTO.getIsbn10())
-                .isbn13(bookDetailsDTO.getIsbn13())
-                .title(bookDetailsDTO.getTitle())
-                .authors(mapToAuthorList(bookDetailsDTO.getAuthors()))
-                .publisher(bookDetailsDTO.getPublisher())
-                .publishedDate(bookDetailsDTO.getPublishedDate())
-                .description(bookDetailsDTO.getDescription())
-                .pages(bookDetailsDTO.getPages())
-                .imageLink(bookDetailsDTO.getImageLink())
-                .build();
-        repository.save(bookEntity);
-    }
-
-    private Set<AuthorEntiy> mapToAuthorList(List<String> authorNameList){
-        return authorNameList.stream()
-                .map(authorName -> AuthorEntiy.builder().name(authorName).build())
-                .collect(Collectors.toUnmodifiableSet());
-    }
-}

src/main/java/io/wkrzywiec/hexagonal/library/infrastructure/repository/PostgresBookRepository.java

@@ -1,8 +0,0 @@
-package io.wkrzywiec.hexagonal.library.infrastructure.repository;
-
-import org.springframework.data.repository.CrudRepository;
-import org.springframework.stereotype.Repository;
-
-@Repository
-public interface PostgresBookRepository extends CrudRepository<BookEntity, Long> {
-}

src/main/java/io/wkrzywiec/hexagonal/library/inventory/InventoryFacade.java

@@ -0,0 +1,30 @@
+package io.wkrzywiec.hexagonal.library.inventory;
+
+import io.wkrzywiec.hexagonal.library.inventory.model.AddNewBookCommand;
+import io.wkrzywiec.hexagonal.library.inventory.model.Book;
+import io.wkrzywiec.hexagonal.library.inventory.model.NewBookWasAddedEvent;
+import io.wkrzywiec.hexagonal.library.inventory.ports.incoming.AddNewBook;
+import io.wkrzywiec.hexagonal.library.inventory.ports.outgoing.InventoryEventPublisher;
+import io.wkrzywiec.hexagonal.library.inventory.ports.outgoing.GetBookDetails;
+import io.wkrzywiec.hexagonal.library.inventory.ports.outgoing.InventoryDatabase;
+
+
+public class InventoryFacade implements AddNewBook{
+
+    private InventoryDatabase database;
+    private GetBookDetails getBookDetails;
+    private InventoryEventPublisher eventPublisher;
+
+    public InventoryFacade(InventoryDatabase database, GetBookDetails getBookDetails, InventoryEventPublisher eventPublisher) {
+        this.database = database;
+        this.getBookDetails = getBookDetails;
+        this.eventPublisher = eventPublisher;
+    }
+
+    @Override
+    public void handle(AddNewBookCommand addNewBookCommand){
+        Book book = getBookDetails.handle(addNewBookCommand.getGoogleBookId());
+        Book savedBook = database.save(book);
+        eventPublisher.publishNewBookWasAddedEvent(new NewBookWasAddedEvent(savedBook.getIdAsLong()));
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/inventory/application/BookCommandController.java

@@ -1,7 +1,7 @@
-package io.wkrzywiec.hexagonal.library.application;
+package io.wkrzywiec.hexagonal.library.inventory.application;
 
-import io.wkrzywiec.hexagonal.library.domain.book.dto.ExternalBookIdDTO;
-import io.wkrzywiec.hexagonal.library.domain.book.ports.incoming.AddNewBook;
+import io.wkrzywiec.hexagonal.library.inventory.model.AddNewBookCommand;
+import io.wkrzywiec.hexagonal.library.inventory.ports.incoming.AddNewBook;
 import lombok.RequiredArgsConstructor;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
@@ -18,8 +18,8 @@ public class BookCommandController {
     private final AddNewBook addNewBook;
 
     @PostMapping("")
-    public ResponseEntity<String> addNewBook(@RequestBody ExternalBookIdDTO externalBookIdDTO){
-        addNewBook.handle(externalBookIdDTO);
+    public ResponseEntity<String> addNewBook(@RequestBody AddNewBookCommand addNewBookCommand){
+        addNewBook.handle(addNewBookCommand);
         return new ResponseEntity<>("New book was added to library", HttpStatus.CREATED);
     }
 }

src/main/java/io/wkrzywiec/hexagonal/library/inventory/infrastructure/BookRepository.java

@@ -0,0 +1,9 @@
+package io.wkrzywiec.hexagonal.library.inventory.infrastructure;
+
+import io.wkrzywiec.hexagonal.library.inventory.model.Book;
+import org.springframework.data.repository.CrudRepository;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public interface BookRepository extends CrudRepository<Book, Long> {
+}

src/main/java/io/wkrzywiec/hexagonal/library/inventory/infrastructure/GoogleBooksAdapter.java

@@ -1,10 +1,14 @@
-package io.wkrzywiec.hexagonal.library.infrastructure.adapter;
+package io.wkrzywiec.hexagonal.library.inventory.infrastructure;
 
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
 import com.google.gson.JsonParser;
-import io.wkrzywiec.hexagonal.library.domain.book.dto.BookDetailsDTO;
-import io.wkrzywiec.hexagonal.library.domain.book.ports.incoming.GetBookDetails;
+import io.wkrzywiec.hexagonal.library.inventory.model.Author;
+import io.wkrzywiec.hexagonal.library.inventory.model.Book;
+import io.wkrzywiec.hexagonal.library.inventory.model.BookIdentification;
+import io.wkrzywiec.hexagonal.library.inventory.model.Isbn10;
+import io.wkrzywiec.hexagonal.library.inventory.model.Isbn13;
+import io.wkrzywiec.hexagonal.library.inventory.ports.outgoing.GetBookDetails;
 import lombok.RequiredArgsConstructor;
 import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpHeaders;
@@ -12,7 +16,6 @@ import org.springframework.http.HttpMethod;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.client.RestTemplate;
 
-import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.stream.Collectors;
@@ -26,10 +29,9 @@ public class GoogleBooksAdapter implements GetBookDetails {
     private final RestTemplate restTemplate;
 
     @Override
-    public BookDetailsDTO handle(String googleBookId) {
+    public Book handle(String googleBookId) {
 
         HttpHeaders requestHeader = new HttpHeaders();
-//        requestHeader.add("Accept", MediaType.ALL_VALUE);
         HttpEntity<Object> requestEntity = new HttpEntity<>(requestHeader);
 
         ResponseEntity<String> responseEntity =
@@ -45,18 +47,19 @@ public class GoogleBooksAdapter implements GetBookDetails {
 
         JsonObject volumeInfo = response.getAsJsonObject("volumeInfo");
 
-        return BookDetailsDTO.builder()
-                .bookExternalId(googleBookId)
-                .isbn10(extractIsbn(volumeInfo, "ISBN_10"))
-                .isbn13(extractIsbn(volumeInfo, "ISBN_13"))
-                .title(volumeInfo.get("title").getAsString())
-                .authors(extractAuthors(volumeInfo))
-                .publisher(volumeInfo.get("publisher").getAsString())
-                .publishedDate(volumeInfo.get("publishedDate").getAsString())
-                .description(volumeInfo.get("description").getAsString())
-                .pages(volumeInfo.get("pageCount").getAsInt())
-                .imageLink(extractImage(volumeInfo))
-                .build();
+        Isbn10 isbn10 = new Isbn10(extractIsbn(volumeInfo, "ISBN_10"));
+        Isbn13 isbn13 = new Isbn13(extractIsbn(volumeInfo, "ISBN_13"));
+
+        return new Book(
+                new BookIdentification(googleBookId, isbn10, isbn13),
+                volumeInfo.get("title").getAsString(),
+                extractAuthors(volumeInfo),
+                volumeInfo.get("publisher").getAsString(),
+                volumeInfo.get("publishedDate").getAsString(),
+                volumeInfo.get("description").getAsString(),
+                volumeInfo.get("pageCount").getAsInt(),
+                extractImage(volumeInfo)
+        );
     }
 
     private String extractIsbn(JsonObject volumeInfo, String isbnType) {
@@ -73,7 +76,7 @@ public class GoogleBooksAdapter implements GetBookDetails {
                 .orElseThrow(() -> new RuntimeException("Inside volumeInfo there is no " + isbnType));
     }
 
-    private List<String> extractAuthors(JsonObject volumeInfo) {
+    private Set<Author> extractAuthors(JsonObject volumeInfo) {
         return StreamSupport.stream(
                 ofNullable(volumeInfo)
                         .map(volume -> volume.getAsJsonArray("authors"))
@@ -81,7 +84,8 @@ public class GoogleBooksAdapter implements GetBookDetails {
                         .spliterator(),
                 false)
                 .map(JsonElement::getAsString)
-                .collect(Collectors.toList());
+                .map(Author::new)
+                .collect(Collectors.toSet());
     }
 
     private String extractImage(JsonObject volumeInfo) {

src/main/java/io/wkrzywiec/hexagonal/library/inventory/infrastructure/InventoryDatabaseAdapter.java

@@ -0,0 +1,16 @@
+package io.wkrzywiec.hexagonal.library.inventory.infrastructure;
+
+import io.wkrzywiec.hexagonal.library.inventory.model.Book;
+import io.wkrzywiec.hexagonal.library.inventory.ports.outgoing.InventoryDatabase;
+import lombok.RequiredArgsConstructor;
+
+@RequiredArgsConstructor
+public class InventoryDatabaseAdapter implements InventoryDatabase {
+
+    private final BookRepository repository;
+
+    @Override
+    public Book save(Book book) {
+        return repository.save(book);
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/inventory/infrastructure/SpringInventoryEventPublisherAdapter.java

@@ -0,0 +1,17 @@
+package io.wkrzywiec.hexagonal.library.inventory.infrastructure;
+
+import io.wkrzywiec.hexagonal.library.inventory.model.NewBookWasAddedEvent;
+import io.wkrzywiec.hexagonal.library.inventory.ports.outgoing.InventoryEventPublisher;
+import lombok.RequiredArgsConstructor;
+import org.springframework.context.ApplicationEventPublisher;
+
+@RequiredArgsConstructor
+public class SpringInventoryEventPublisherAdapter implements InventoryEventPublisher {
+
+    private final ApplicationEventPublisher applicationEventPublisher;
+
+    @Override
+    public void publishNewBookWasAddedEvent(NewBookWasAddedEvent event) {
+        applicationEventPublisher.publishEvent(event);
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/inventory/model/AddNewBookCommand.java

@@ -1,15 +1,15 @@
-package io.wkrzywiec.hexagonal.library.domain.book.dto;
+package io.wkrzywiec.hexagonal.library.inventory.model;
 
 import lombok.AllArgsConstructor;
 import lombok.Builder;
 import lombok.Data;
+import lombok.Getter;
 import lombok.NoArgsConstructor;
 
-@Data
+@Getter
 @AllArgsConstructor
 @NoArgsConstructor
 @Builder
-public class ExternalBookIdDTO {
-
-    private String value;
+public class AddNewBookCommand {
+    private String googleBookId;
 }

src/main/java/io/wkrzywiec/hexagonal/library/inventory/model/Author.java

@@ -1,6 +1,7 @@
-package io.wkrzywiec.hexagonal.library.infrastructure.repository;
+package io.wkrzywiec.hexagonal.library.inventory.model;
 
-import lombok.Builder;
+import lombok.EqualsAndHashCode;
+import lombok.ToString;
 
 import javax.persistence.Column;
 import javax.persistence.Entity;
@@ -9,10 +10,11 @@ import javax.persistence.GenerationType;
 import javax.persistence.Id;
 import javax.persistence.Table;
 
-@Builder
 @Entity
 @Table(name="author")
-public class AuthorEntiy {
+@EqualsAndHashCode
+@ToString
+public class Author {
 
     @Id
     @GeneratedValue(strategy= GenerationType.IDENTITY)
@@ -21,4 +23,11 @@ public class AuthorEntiy {
 
     @Column(name="name", unique=true)
     private String name;
+
+    public Author(String name) {
+        this.name = name;
+    }
+
+    private Author() {
+    }
 }

src/main/java/io/wkrzywiec/hexagonal/library/inventory/model/Book.java

@@ -1,13 +1,10 @@
-package io.wkrzywiec.hexagonal.library.infrastructure.repository;
+package io.wkrzywiec.hexagonal.library.inventory.model;
 
-import lombok.AllArgsConstructor;
-import lombok.Builder;
-import lombok.Getter;
-import lombok.NoArgsConstructor;
-import lombok.Setter;
+import lombok.EqualsAndHashCode;
 
 import javax.persistence.CascadeType;
 import javax.persistence.Column;
+import javax.persistence.Embedded;
 import javax.persistence.Entity;
 import javax.persistence.FetchType;
 import javax.persistence.GeneratedValue;
@@ -17,31 +14,20 @@ import javax.persistence.JoinColumn;
 import javax.persistence.JoinTable;
 import javax.persistence.ManyToMany;
 import javax.persistence.Table;
-
 import java.util.Set;
 
 
-@Builder
 @Entity
-@AllArgsConstructor
-@NoArgsConstructor
-@Setter
-@Getter
 @Table(name="book")
-public class BookEntity {
+@EqualsAndHashCode
+public class Book {
 
     @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     private Long id;
 
-    @Column(name="book_external_id")
-    private String bookExternalId;
-
-    @Column(name="isbn_10")
-    private String isbn10;
-
-    @Column(name="isbn_13")
-    private String isbn13;
+    @Embedded
+    private BookIdentification identification;
 
     @Column(name="title")
     private String title;
@@ -52,7 +38,7 @@ public class BookEntity {
             name="book_author",
             joinColumns=@JoinColumn(name="book_id"),
             inverseJoinColumns=@JoinColumn(name="author_id"))
-    private Set<AuthorEntiy> authors;
+    private Set<Author> authors;
 
     @Column(name="publisher")
     private String publisher;
@@ -63,9 +49,28 @@ public class BookEntity {
     @Column(name="description", columnDefinition="TEXT")
     private String description;
 
-    @Column(name="pages")
+    @Column(name="page_count")
     private int pages;
 
     @Column(name="imageLink", columnDefinition="TEXT")
+    @EqualsAndHashCode.Exclude
     private String imageLink;
+
+    public Book(BookIdentification identification, String title, Set<Author> authors, String publisher, String publishedDate, String description, int pages, String imageLink) {
+        this.identification = identification;
+        this.title = title;
+        this.authors = authors;
+        this.publisher = publisher;
+        this.publishedDate = publishedDate;
+        this.description = description;
+        this.pages = pages;
+        this.imageLink = imageLink;
+    }
+
+    public Long getIdAsLong(){
+        return id;
+    }
+
+    private Book() {
+    }
 }

src/main/java/io/wkrzywiec/hexagonal/library/inventory/model/BookIdentification.java

@@ -0,0 +1,30 @@
+package io.wkrzywiec.hexagonal.library.inventory.model;
+
+import lombok.EqualsAndHashCode;
+
+import javax.persistence.Column;
+import javax.persistence.Embeddable;
+import javax.persistence.Embedded;
+
+@Embeddable
+@EqualsAndHashCode
+public class BookIdentification {
+
+    @Column(name="book_external_id")
+    private String bookExternalId;
+
+    @Embedded
+    private Isbn10 isbn10;
+
+    @Embedded
+    private Isbn13 isbn13;
+
+    public BookIdentification(String bookExternalId, Isbn10 isbn10, Isbn13 isbn13) {
+        this.bookExternalId = bookExternalId;
+        this.isbn10 = isbn10;
+        this.isbn13 = isbn13;
+    }
+
+    private BookIdentification() {
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/inventory/model/Isbn10.java

@@ -0,0 +1,28 @@
+package io.wkrzywiec.hexagonal.library.inventory.model;
+
+import lombok.EqualsAndHashCode;
+
+import javax.persistence.Column;
+import javax.persistence.Embeddable;
+
+@EqualsAndHashCode
+@Embeddable
+public class Isbn10 {
+    @Column(name="isbn_10")
+    private String value;
+
+    public Isbn10(String value) {
+        if (value.matches("\\d{10}")){
+            this.value = value;
+        } else {
+            throw new IllegalArgumentException("ISBN-10 should have 10 digits only.");
+        }
+    }
+
+    private Isbn10() {
+    }
+
+    public String getAsString(){
+        return value;
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/inventory/model/Isbn13.java

@@ -0,0 +1,30 @@
+package io.wkrzywiec.hexagonal.library.inventory.model;
+
+import lombok.EqualsAndHashCode;
+import lombok.ToString;
+
+import javax.persistence.Column;
+import javax.persistence.Embeddable;
+
+@EqualsAndHashCode
+@Embeddable
+public class Isbn13 {
+
+    @Column(name="isbn_13")
+    private String value;
+
+    public Isbn13(String value) {
+        if (value.matches("\\d{13}")){
+            this.value = value;
+        } else {
+            throw new IllegalArgumentException("ISBN-13 should have 10 digits only.");
+        }
+    }
+
+    private Isbn13() {
+    }
+
+    public String getAsString(){
+        return value;
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/inventory/model/NewBookWasAddedEvent.java

@@ -0,0 +1,22 @@
+package io.wkrzywiec.hexagonal.library.inventory.model;
+
+import java.time.Instant;
+
+public class NewBookWasAddedEvent {
+
+    private final Long bookId;
+    private final Instant timestamp;
+
+    public NewBookWasAddedEvent(Long bookId) {
+        this.bookId = bookId;
+        timestamp = Instant.now();
+    }
+
+    public Long getBookIdAsLong() {
+        return bookId;
+    }
+
+    public String getEventTimeStampAsString() {
+        return timestamp.toString();
+    }
+}

src/main/java/io/wkrzywiec/hexagonal/library/inventory/ports/incoming/AddNewBook.java

@@ -0,0 +1,7 @@
+package io.wkrzywiec.hexagonal.library.inventory.ports.incoming;
+
+import io.wkrzywiec.hexagonal.library.inventory.model.AddNewBookCommand;
+
+public interface AddNewBook {
+    void handle(AddNewBookCommand addNewBookCommand);
+}

src/main/java/io/wkrzywiec/hexagonal/library/inventory/ports/outgoing/GetBookDetails.java

@@ -0,0 +1,7 @@
+package io.wkrzywiec.hexagonal.library.inventory.ports.outgoing;
+
+import io.wkrzywiec.hexagonal.library.inventory.model.Book;
+
+public interface GetBookDetails {
+    Book handle(String bookId);
+}

src/main/java/io/wkrzywiec/hexagonal/library/inventory/ports/outgoing/InventoryDatabase.java

@@ -0,0 +1,7 @@
+package io.wkrzywiec.hexagonal.library.inventory.ports.outgoing;
+
+import io.wkrzywiec.hexagonal.library.inventory.model.Book;
+
+public interface InventoryDatabase {
+    Book save(Book book);
+}

src/main/java/io/wkrzywiec/hexagonal/library/inventory/ports/outgoing/InventoryEventPublisher.java

@@ -0,0 +1,7 @@
+package io.wkrzywiec.hexagonal.library.inventory.ports.outgoing;
+
+import io.wkrzywiec.hexagonal.library.inventory.model.NewBookWasAddedEvent;
+
+public interface InventoryEventPublisher {
+    void publishNewBookWasAddedEvent(NewBookWasAddedEvent event);
+}

src/main/resources/application-h2.yml

@@ -0,0 +1,9 @@
+spring:
+  application:
+    name: library
+  datasource:
+    url: jdbc:h2:mem:testdb
+    driverClassName: org.h2.Driver
+    username: sa
+    password: password
+    jpa.database-platform: org.hibernate.dialect.H2Dialect

src/main/resources/application-postgres.yml

@@ -0,0 +1,9 @@
+spring:
+  application:
+    name: library
+  datasource:
+    url: jdbc:postgresql://localhost:5432/library
+    driverClassName: org.postgresql.Driver
+    username: library
+    password: library
+    jpa.database-platform: org.hibernate.dialect.PostgreSQL9Dialect

src/main/resources/application.yml

@@ -2,8 +2,8 @@ spring:
   application:
     name: library
   datasource:
-    url: jdbc:h2:mem:testdb
-    driverClassName: org.h2.Driver
-    username: sa
-    password: password
-    jpa.database-platform: org.hibernate.dialect.H2Dialect
+    url: jdbc:postgresql://${POSTGRES_SERVER}:5432/${POSTGRES_DB}
+    driverClassName: org.postgresql.Driver
+    username: ${POSTGRES_USER}
+    password: ${POSTGRES_PASSWORD}
+    jpa.database-platform: org.hibernate.dialect.PostgreSQL9Dialect

src/main/resources/db/changelog/01_books_and_authors.sql

@@ -0,0 +1,23 @@
+CREATE TABLE IF NOT EXISTS public.book (
+    id                  BIGSERIAL PRIMARY KEY,
+    book_external_id    CHARACTER VARYING(255) NOT NULL UNIQUE,
+    isbn_10             CHARACTER VARYING(10) DEFAULT NULL,
+    isbn_13             CHARACTER VARYING(13) DEFAULT NULL,
+    title               CHARACTER VARYING(255) NOT NULL,
+    publisher           CHARACTER VARYING(255) DEFAULT NULL,
+    published_date      CHARACTER VARYING(255) DEFAULT NULL,
+    description         TEXT DEFAULT NULL,
+    page_count          INTEGER DEFAULT NULL,
+    image_link          CHARACTER VARYING(1000) DEFAULT NULL
+);
+
+CREATE TABLE IF NOT EXISTS public.author (
+    id          BIGSERIAL PRIMARY KEY,
+    name        CHARACTER VARYING(255) NOT NULL UNIQUE
+);
+
+CREATE TABLE IF NOT EXISTS public.book_author (
+    id          BIGSERIAL PRIMARY KEY,
+    book_id     BIGINT NOT NULL REFERENCES public.book,
+    author_id   BIGINT NOT NULL REFERENCES public.author
+);

src/main/resources/db/changelog/02_users.sql

@@ -0,0 +1,6 @@
+CREATE TABLE IF NOT EXISTS public.user (
+    id          BIGSERIAL PRIMARY KEY,
+    first_name  CHARACTER VARYING(255) NOT NULL,
+    last_name   CHARACTER VARYING(255) NOT NULL,
+    email       CHARACTER VARYING(255) NOT NULL UNIQUE
+);

src/main/resources/db/changelog/03_books_statuses.sql

@@ -0,0 +1,16 @@
+CREATE TABLE IF NOT EXISTS public.available (
+    id          BIGSERIAL PRIMARY KEY,
+    book_id     BIGINT NOT NULL REFERENCES public.book
+);
+
+CREATE TABLE IF NOT EXISTS public.reserved (
+    id          BIGSERIAL PRIMARY KEY,
+    book_id     BIGINT NOT NULL REFERENCES public.book,
+    user_id     BIGINT NOT NULL REFERENCES public.user
+);
+
+CREATE TABLE IF NOT EXISTS public.borrowed (
+    id          BIGSERIAL PRIMARY KEY,
+    book_id     BIGINT NOT NULL REFERENCES public.book,
+    user_id     BIGINT NOT NULL REFERENCES public.user
+);

src/main/resources/db/changelog/db.changelog-master.yaml

@@ -0,0 +1,31 @@
+databaseChangeLog:
+  - changeSet:
+      id: 1
+      author: Wojtek
+      comment: Create tables for books and authors
+      changes:
+        - sqlFile:
+            path: 01_books_and_authors.sql
+            relativeToChangelogFile: true
+            splitStatements: true
+            stripComments: true
+  - changeSet:
+      id: 2
+      author: Wojtek
+      comment: Create table for users
+      changes:
+        - sqlFile:
+            path: 02_users.sql
+            relativeToChangelogFile: true
+            splitStatements: true
+            stripComments: true
+  - changeSet:
+      id: 3
+      author: Wojtek
+      comment: Create tables for books statuses (available, reserved, borrowed)
+      changes:
+        - sqlFile:
+            path: 03_books_statuses.sql
+            relativeToChangelogFile: true
+            splitStatements: true
+            stripComments: true

src/test/java/io/wkrzywiec/hexagonal/library/TestData.java

@@ -1,24 +1,37 @@
 package io.wkrzywiec.hexagonal.library;
 
-import io.wkrzywiec.hexagonal.library.domain.book.dto.BookDetailsDTO;
+import io.wkrzywiec.hexagonal.library.inventory.model.Author;
+import io.wkrzywiec.hexagonal.library.inventory.model.Book;
+import io.wkrzywiec.hexagonal.library.inventory.model.BookIdentification;
+import io.wkrzywiec.hexagonal.library.inventory.model.Isbn10;
+import io.wkrzywiec.hexagonal.library.inventory.model.Isbn13;
 
 import java.util.Collections;
 
 public class TestData {
 
-    public static BookDetailsDTO homoDeusBookDetailsDTO() {
-        return BookDetailsDTO
-                .builder()
-                .bookExternalId("dWYyCwAAQBAJ")
-                .isbn10("1473545374")
-                .isbn13("9781473545373")
-                .title("Homo Deus")
-                .authors(Collections.singletonList("Yuval Noah Harari"))
-                .publisher("Random House")
-                .publishedDate("2016-09-08")
-                .description("<p><b>**THE MILLION COPY BESTSELLER**</b><br> <b></b><br><b> <i>Sapiens </i>showed us where we came from. In uncertain times, <i>Homo Deus</i> shows us where we’re going.</b></p><p> Yuval Noah Harari envisions a near future in which we face a new set of challenges. <i>Homo Deus</i> explores the projects, dreams and nightmares that will shape the twenty-first century and beyond – from overcoming death to creating artificial life.</p><p> It asks the fundamental questions: how can we protect this fragile world from our own destructive power? And what does our future hold?<br> <b></b><br><b> '<i>Homo Deus</i> will shock you. It will entertain you. It will make you think in ways you had not thought before’ Daniel Kahneman, bestselling author of <i>Thinking, Fast and Slow</i></b></p>")
-                .pages(528)
-                .build();
+    public static String homoDeusBookGoogleId() {
+        return "dWYyCwAAQBAJ";
+    }
+
+    public static String homoDeusBookTitle() {
+        return "Homo Deus";
+    }
+
+    public static Book homoDeusBook() {
+        Isbn10 isbn10 = new Isbn10("1473545374");
+        Isbn13 isbn13 = new Isbn13("9781473545373");
+
+        return new Book(
+                new BookIdentification(homoDeusBookGoogleId(), isbn10, isbn13),
+                homoDeusBookTitle(),
+                Collections.singleton(new Author("Yuval Noah Harari")),
+                "Random House",
+                "2016-09-08",
+                "<p><b>**THE MILLION COPY BESTSELLER**</b><br> <b></b><br><b> <i>Sapiens </i>showed us where we came from. In uncertain times, <i>Homo Deus</i> shows us where we’re going.</b></p><p> Yuval Noah Harari envisions a near future in which we face a new set of challenges. <i>Homo Deus</i> explores the projects, dreams and nightmares that will shape the twenty-first century and beyond – from overcoming death to creating artificial life.</p><p> It asks the fundamental questions: how can we protect this fragile world from our own destructive power? And what does our future hold?<br> <b></b><br><b> '<i>Homo Deus</i> will shock you. It will entertain you. It will make you think in ways you had not thought before’ Daniel Kahneman, bestselling author of <i>Thinking, Fast and Slow</i></b></p>",
+                528,
+                        "http://books.google.com/books/content?id=dWYyCwAAQBAJ&printsec=frontcover&img=1&zoom=1&edge=curl&imgtk=AFLRE73PkLs4TNB-W2uhDvXJkIB4-9G9AJ_L1iYTYLEXa3zi2kahdsN9-_0tL7WRWgujNpjMA5ZuJO7_ykFUlCWAyLzcQVcGkqUS-NOkUkEcJ_ZRrgq48URpcfBrJWQCwSWtHo5pEGkp&source=gbs_api"
+        );
     }
 
     public static String homoDeusGooleBooksResponse(){

src/test/java/io/wkrzywiec/hexagonal/library/architecture/BorrowingArchitectureTest.java

@@ -0,0 +1,29 @@
+package io.wkrzywiec.hexagonal.library.architecture;
+
+import com.tngtech.archunit.core.importer.ImportOption;
+import com.tngtech.archunit.junit.AnalyzeClasses;
+import com.tngtech.archunit.junit.ArchTest;
+import com.tngtech.archunit.lang.ArchRule;
+import io.wkrzywiec.hexagonal.library.borrowing.BorrowingFacade;
+
+import static com.tngtech.archunit.lang.syntax.ArchRuleDefinition.noClass;
+import static com.tngtech.archunit.library.Architectures.onionArchitecture;
+
+@AnalyzeClasses(packages = {"io.wkrzywiec.hexagonal.library.borrowing"},
+                importOptions = { ImportOption.DoNotIncludeTests.class })
+public class BorrowingArchitectureTest {
+
+    @ArchTest
+    public static final ArchRule hexagonalArchInBorrowingDomain = onionArchitecture()
+            .domainModels("io.wkrzywiec.hexagonal.library.borrowing.model..")
+            .domainServices("io.wkrzywiec.hexagonal.library.borrowing..")
+            .applicationServices("io.wkrzywiec.hexagonal.library.borrowing.application..")
+            .adapter("infrastructure", "io.wkrzywiec.hexagonal.library.borrowing.infrastructure..");
+
+    @ArchTest
+    public static final ArchRule noSpringDependenciesInBorrowingFacade =
+            noClass(BorrowingFacade.class)
+                    .should()
+                    .dependOnClassesThat()
+                    .resideInAPackage("org.springframework..");
+}

src/test/java/io/wkrzywiec/hexagonal/library/architecture/HexagonalArchitectureTest.java

@@ -1,18 +0,0 @@
-package io.wkrzywiec.hexagonal.library.architecture;
-
-import com.tngtech.archunit.junit.AnalyzeClasses;
-import com.tngtech.archunit.junit.ArchTest;
-import com.tngtech.archunit.lang.ArchRule;
-
-import static com.tngtech.archunit.lang.syntax.ArchRuleDefinition.noClasses;
-
-@AnalyzeClasses(packages = "io.wkrzywiec.hexagonal.library.domain")
-public class HexagonalArchitectureTest {
-
-    @ArchTest
-    public static final ArchRule noSpringDependenciesInDomainPackage =
-            noClasses().that()
-                    .resideInAPackage("..io.wkrzywiec.hexagonal.library.domain..")
-            .should()
-            .dependOnClassesThat().resideInAPackage("org.springframework..");
-}

src/test/java/io/wkrzywiec/hexagonal/library/architecture/InventoryArchitectureTest.java

@@ -0,0 +1,30 @@
+package io.wkrzywiec.hexagonal.library.architecture;
+
+import com.tngtech.archunit.core.importer.ImportOption;
+import com.tngtech.archunit.junit.AnalyzeClasses;
+import com.tngtech.archunit.junit.ArchTest;
+import com.tngtech.archunit.lang.ArchRule;
+import io.wkrzywiec.hexagonal.library.inventory.InventoryFacade;
+
+import static com.tngtech.archunit.lang.syntax.ArchRuleDefinition.noClass;
+import static com.tngtech.archunit.library.Architectures.onionArchitecture;
+
+@AnalyzeClasses(packages = {"io.wkrzywiec.hexagonal.library.inventory"},
+        importOptions = { ImportOption.DoNotIncludeTests.class })
+public class InventoryArchitectureTest {
+
+    @ArchTest
+    public static final ArchRule hexagonalArchInInventoryDomain = onionArchitecture()
+            .domainModels("io.wkrzywiec.hexagonal.library.inventory.model..")
+            .domainServices("io.wkrzywiec.hexagonal.library.inventory..")
+            .applicationServices("io.wkrzywiec.hexagonal.library.inventory.application..")
+            .adapter("infrastructure", "io.wkrzywiec.hexagonal.library.inventory.infrastructure..");
+
+    @ArchTest
+    public static final ArchRule noSpringDependenciesInInventoryFacade =
+            noClass(InventoryFacade.class)
+                    .should()
+                    .dependOnClassesThat()
+                    .resideInAPackage("org.springframework..");
+
+}

src/test/java/io/wkrzywiec/hexagonal/library/borrowing/BorrowingFacadeTest.java

@@ -0,0 +1,125 @@
+package io.wkrzywiec.hexagonal.library.borrowing;
+
+import io.wkrzywiec.hexagonal.library.borrowing.model.ActiveUser;
+import io.wkrzywiec.hexagonal.library.borrowing.model.AvailableBook;
+import io.wkrzywiec.hexagonal.library.borrowing.model.BookReservationCommand;
+import io.wkrzywiec.hexagonal.library.borrowing.model.MakeBookAvailableCommand;
+import io.wkrzywiec.hexagonal.library.borrowing.model.exception.ActiveUserNotFoundException;
+import io.wkrzywiec.hexagonal.library.borrowing.model.exception.AvailableBookNotFoundExeption;
+import io.wkrzywiec.hexagonal.library.borrowing.model.exception.TooManyBooksAssignedToUserException;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class BorrowingFacadeTest {
+
+    private BorrowingFacade facade;
+    private InMemoryBorrowingDatabase database;
+
+    @BeforeEach
+    public void init(){
+        database = new InMemoryBorrowingDatabase();
+        facade = new BorrowingFacade(database);
+    }
+
+    @Test
+    @DisplayName("Make book available")
+    public void whenMakeBookAvailableCommandReceived_thenBookIsOnAvailableStatus() {
+        //given
+        MakeBookAvailableCommand makeBookAvailableCommand =
+                MakeBookAvailableCommand.builder()
+                        .bookId(100L)
+                        .build();
+
+        //when
+        facade.handle(makeBookAvailableCommand);
+
+        //then
+        assertTrue(database.availableBooks.containsKey(100L));
+        assertTrue(database.availableBooks.containsValue(new AvailableBook(100L)));
+    }
+
+    @Test
+    @DisplayName("Make successful book reservation")
+    public void givenAvailableBooksAndActiveUser_whenMakingReservation_thenBookIsReserved(){
+        //given
+        BookReservationCommand reservationCommand = ReservationTestData.anyBookReservation(100L, 100L);
+        AvailableBook availableBook = ReservationTestData.anyAvailableBook(reservationCommand.getBookId());
+        ActiveUser activeUser = ReservationTestData.anyActiveUser(reservationCommand.getUserId());
+
+        database.activeUsers.put(activeUser.getIdAsLong(), activeUser);
+        database.availableBooks.put(availableBook.getIdAsLong(), availableBook);
+
+        //when
+        facade.handle(reservationCommand);
+
+        //then
+        assertEquals(1, activeUser.getReservedBookList().size());
+        assertEquals(availableBook.getIdAsLong(), activeUser.getReservedBookList().get(0).getIdAsLong());
+    }
+
+    @Test
+    @DisplayName("User can't have more than 3 reservations")
+    public void givenActiveUserAlreadyHas3Books_whenMakingReservation_thenBookIsNotReserved(){
+        //given
+        BookReservationCommand firstReservationCommand = ReservationTestData.anyBookReservation(100L, 100L);
+        BookReservationCommand secondReservationCommand = ReservationTestData.anyBookReservation(101L, 100L);
+        BookReservationCommand thirdReservationCommand = ReservationTestData.anyBookReservation(102L, 100L);
+        BookReservationCommand fourthReservationCommand = ReservationTestData.anyBookReservation(103L, 100L);
+
+        AvailableBook availableBookNo1 = ReservationTestData.anyAvailableBook(firstReservationCommand.getBookId());
+        AvailableBook availableBookNo2 = ReservationTestData.anyAvailableBook(secondReservationCommand.getBookId());
+        AvailableBook availableBookNo3 = ReservationTestData.anyAvailableBook(thirdReservationCommand.getBookId());
+        AvailableBook availableBookNo4 = ReservationTestData.anyAvailableBook(fourthReservationCommand.getBookId());
+
+        ActiveUser activeUser = ReservationTestData.anyActiveUser(firstReservationCommand.getUserId());
+
+        database.availableBooks.put(availableBookNo1.getIdAsLong(), availableBookNo1);
+        database.availableBooks.put(availableBookNo2.getIdAsLong(), availableBookNo2);
+        database.availableBooks.put(availableBookNo3.getIdAsLong(), availableBookNo3);
+        database.availableBooks.put(availableBookNo4.getIdAsLong(), availableBookNo4);
+        database.activeUsers.put(activeUser.getIdAsLong(), activeUser);
+
+        facade.handle(firstReservationCommand);
+        facade.handle(secondReservationCommand);
+        facade.handle(thirdReservationCommand);
+
+        //when & then
+        assertThrows(
+                TooManyBooksAssignedToUserException.class,
+                () -> facade.handle(fourthReservationCommand));
+    }
+
+    @Test
+    @DisplayName("Try to reserve book,but it's not available")
+    public void givenNotAvailableBook_whenMakingReservation_thenThrowException(){
+        //given
+        BookReservationCommand reservationCommand = ReservationTestData.anyBookReservation(100L, 100L);
+        ActiveUser activeUser = ReservationTestData.anyActiveUser(reservationCommand.getUserId());
+
+        database.activeUsers.put(activeUser.getIdAsLong(), activeUser);
+
+        assertThrows(
+                AvailableBookNotFoundExeption.class,
+                () -> facade.handle(reservationCommand));
+    }
+
+    @Test
+    @DisplayName("Try to reserve book, but active user is not found")
+    public void givenNotActiveUser_whenMakingReservation_thenThrowException(){
+        //given
+        BookReservationCommand reservationCommand = ReservationTestData.anyBookReservation(100L, 100L);
+        AvailableBook availableBook = ReservationTestData.anyAvailableBook(reservationCommand.getBookId());
+
+        database.availableBooks.put(availableBook.getIdAsLong(), availableBook);
+
+        //when & then
+        assertThrows(
+                ActiveUserNotFoundException.class,
+                () -> facade.handle(reservationCommand));
+    }
+}

src/test/java/io/wkrzywiec/hexagonal/library/borrowing/InMemoryBorrowingDatabase.java

@@ -0,0 +1,50 @@
+package io.wkrzywiec.hexagonal.library.borrowing;
+
+import io.wkrzywiec.hexagonal.library.borrowing.model.ActiveUser;
+import io.wkrzywiec.hexagonal.library.borrowing.model.AvailableBook;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ReservationDetails;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ReservationId;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ReservedBook;
+import io.wkrzywiec.hexagonal.library.borrowing.ports.outgoing.BorrowingDatabase;
+
+import java.util.Optional;
+import java.util.Random;
+import java.util.concurrent.ConcurrentHashMap;
+
+public class InMemoryBorrowingDatabase implements BorrowingDatabase {
+
+    ConcurrentHashMap<Long, ActiveUser> activeUsers = new ConcurrentHashMap<>();
+    ConcurrentHashMap<Long, AvailableBook> availableBooks = new ConcurrentHashMap<>();
+    ConcurrentHashMap<Long, ReservedBook> reservedBooks = new ConcurrentHashMap<>();
+
+    @Override
+    public void setBookAvailable(Long bookId) {
+        availableBooks.put(bookId, new AvailableBook(bookId));
+    }
+
+    @Override
+    public Optional<AvailableBook> getAvailableBook(Long bookId) {
+        if (availableBooks.containsKey(bookId)) {
+            return Optional.of(availableBooks.get(bookId));
+        } else {
+            return Optional.empty();
+        }
+    }
+
+    @Override
+    public Optional<ActiveUser> getActiveUser(Long userId) {
+        if (activeUsers.containsKey(userId)) {
+            return Optional.of(activeUsers.get(userId));
+        } else {
+            return Optional.empty();
+        }
+    }
+
+    @Override
+    public ReservationDetails save(ReservedBook reservedBook) {
+        Long reservationId = new Random().nextLong();
+        availableBooks.remove(reservedBook.getIdAsLong());
+        reservedBooks.put(reservationId,  reservedBook);
+        return new ReservationDetails(new ReservationId(reservationId), reservedBook);
+    }
+}

src/test/java/io/wkrzywiec/hexagonal/library/borrowing/ReservationTestData.java

@@ -0,0 +1,26 @@
+package io.wkrzywiec.hexagonal.library.borrowing;
+
+import io.wkrzywiec.hexagonal.library.borrowing.model.ActiveUser;
+import io.wkrzywiec.hexagonal.library.borrowing.model.AvailableBook;
+import io.wkrzywiec.hexagonal.library.borrowing.model.BookReservationCommand;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ReservedBook;
+
+import java.util.ArrayList;
+
+public class ReservationTestData {
+
+    public static BookReservationCommand anyBookReservation(Long bookId, Long userId){
+        return BookReservationCommand.builder()
+                .bookId(bookId)
+                .userId(userId)
+                .build();
+    }
+
+    public static AvailableBook anyAvailableBook(Long bookId){
+        return new AvailableBook(bookId);
+    }
+
+    public static ActiveUser anyActiveUser(Long userId){
+        return new ActiveUser(userId, new ArrayList<ReservedBook>());
+    }
+}

src/test/java/io/wkrzywiec/hexagonal/library/borrowing/infrastructure/BorrowingDatabaseAdapterITCase.java

@@ -0,0 +1,127 @@
+package io.wkrzywiec.hexagonal.library.borrowing.infrastructure;
+
+import io.wkrzywiec.hexagonal.library.TestData;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ActiveUser;
+import io.wkrzywiec.hexagonal.library.borrowing.model.AvailableBook;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ReservationDetails;
+import io.wkrzywiec.hexagonal.library.borrowing.model.ReservedBook;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.jdbc.JdbcTest;
+import org.springframework.jdbc.core.JdbcTemplate;
+
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+@JdbcTest
+public class BorrowingDatabaseAdapterITCase {
+
+    @Autowired
+    private JdbcTemplate jdbcTemplate;
+
+    private BorrowingDatabaseAdapter database;
+
+    @BeforeEach
+    public void init(){
+        database = new BorrowingDatabaseAdapter(jdbcTemplate);
+
+        jdbcTemplate.update(
+                "INSERT INTO book (book_external_id, title) VALUES (?, ?)",
+                TestData.homoDeusBookGoogleId(),
+                TestData.homoDeusBookTitle());
+
+        jdbcTemplate.update(
+                "INSERT INTO user (first_name, last_name, email) VALUES (?, ?, ?)",
+                "John",
+                "Doe",
+                "john.doe@test.com");
+    }
+
+    @Test
+    @DisplayName("Save book as available")
+    public void shouldSaveAvailableBook(){
+        //given
+        Long bookId = jdbcTemplate.queryForObject(
+                "SELECT id FROM book WHERE title = ?",
+                Long.class,
+                TestData.homoDeusBookTitle());
+
+        //when
+        database.setBookAvailable(bookId);
+
+        //then
+        Long savedBookId = jdbcTemplate.queryForObject(
+                "SELECT book_id FROM available WHERE book_id = ?",
+                Long.class,
+                bookId);
+        assertEquals(bookId, savedBookId);
+    }
+
+    @Test
+    @DisplayName("Get available book by id")
+    public void shouldGetAvailableBook(){
+        //given
+        Long bookId = jdbcTemplate.queryForObject(
+                "SELECT id FROM book WHERE title = ?",
+                Long.class,
+                TestData.homoDeusBookTitle());
+
+        jdbcTemplate.update(
+                "INSERT INTO available (book_id) VALUES (?)",
+                bookId);
+
+        //when
+        Optional<AvailableBook> availableBookOptional = database.getAvailableBook(bookId);
+
+        //then
+        assertTrue(availableBookOptional.isPresent());
+        assertEquals(bookId, availableBookOptional.get().getIdAsLong());
+    }
+
+    @Test
+    @DisplayName("Get active user by id")
+    public void shouldGetActiveUser() {
+        //given
+        Long activeUserId = jdbcTemplate.queryForObject(
+                "SELECT id FROM user WHERE email = ?",
+                Long.class,
+                "john.doe@test.com");
+
+        //when
+        Optional<ActiveUser> activeUserOptional = database.getActiveUser(activeUserId);
+
+        //then
+        assertTrue(activeUserOptional.isPresent());
+        assertEquals(activeUserId, activeUserOptional.get().getIdAsLong());
+    }
+
+    @Test
+    @DisplayName("Save reserved book")
+    public void shouldSaveReservedBook(){
+        //given
+        Long bookId = jdbcTemplate.queryForObject(
+                "SELECT id FROM book WHERE title = ?",
+                Long.class,
+                TestData.homoDeusBookTitle());
+
+        Long activeUserId = jdbcTemplate.queryForObject(
+                "SELECT id FROM user WHERE email = ?",
+                Long.class,
+                "john.doe@test.com");
+
+        ReservedBook reservedBook = new ReservedBook(bookId, activeUserId);
+
+        //when
+        ReservationDetails reservationDetails = database.save(reservedBook);
+
+        //then
+
+        assertEquals(bookId, reservationDetails.getReservedBook().getIdAsLong());
+        assertEquals(activeUserId, reservationDetails.getReservedBook().getAssignedUserIdAsLong());
+        assertTrue(reservationDetails.getReservationId().getIdAsLong() > 0);
+    }
+}

src/test/java/io/wkrzywiec/hexagonal/library/domain/BookFacadeTest.java

@@ -1,44 +0,0 @@
-package io.wkrzywiec.hexagonal.library.domain;
-
-import io.wkrzywiec.hexagonal.library.TestData;
-import io.wkrzywiec.hexagonal.library.domain.book.BookFacade;
-import io.wkrzywiec.hexagonal.library.domain.book.dto.BookDetailsDTO;
-import io.wkrzywiec.hexagonal.library.domain.book.dto.ExternalBookIdDTO;
-import io.wkrzywiec.hexagonal.library.domain.book.ports.incoming.GetBookDetails;
-import org.junit.jupiter.api.BeforeEach;
-import org.junit.jupiter.api.DisplayName;
-import org.junit.jupiter.api.Test;
-
-import static org.junit.jupiter.api.Assertions.assertEquals;
-
-public class BookFacadeTest {
-
-    private GetBookDetails getBookDetails;
-    private InMemoryBookDatabase database;
-    private BookFacade facade;
-
-    @BeforeEach
-    public void init() {
-        database = new InMemoryBookDatabase();
-        getBookDetails = new GetBookDetailsMock();
-        facade = new BookFacade(database, getBookDetails);
-    }
-
-    @Test
-    @DisplayName("Correctly save a new book in a repository")
-    public void correctlySaveBook(){
-        //given
-        BookDetailsDTO expectedBook = TestData.homoDeusBookDetailsDTO();
-        ExternalBookIdDTO externalBookId = ExternalBookIdDTO
-                .builder()
-                .value(expectedBook.getBookExternalId())
-                .build();
-
-        //when
-        facade.handle(externalBookId);
-
-        //then
-        BookDetailsDTO actualBook = database.books.get(1L);
-        assertEquals(expectedBook, actualBook);
-    }
-}

src/test/java/io/wkrzywiec/hexagonal/library/domain/GetBookDetailsMock.java

@@ -1,23 +0,0 @@
-package io.wkrzywiec.hexagonal.library.domain;
-
-import io.wkrzywiec.hexagonal.library.TestData;
-import io.wkrzywiec.hexagonal.library.domain.book.dto.BookDetailsDTO;
-import io.wkrzywiec.hexagonal.library.domain.book.ports.incoming.GetBookDetails;
-
-import java.util.HashMap;
-import java.util.Map;
-
-public class GetBookDetailsMock implements GetBookDetails {
-
-    private Map<String, BookDetailsDTO> bookDetails;
-
-    public GetBookDetailsMock() {
-        bookDetails = new HashMap<String, BookDetailsDTO>();
-        bookDetails.put(TestData.homoDeusBookDetailsDTO().getBookExternalId(), TestData.homoDeusBookDetailsDTO());
-    }
-
-    @Override
-    public BookDetailsDTO handle(String bookId) {
-        return bookDetails.get(bookId);
-    }
-}

src/test/java/io/wkrzywiec/hexagonal/library/domain/InMemoryBookDatabase.java

@@ -1,18 +0,0 @@
-package io.wkrzywiec.hexagonal.library.domain;
-
-import io.wkrzywiec.hexagonal.library.domain.book.dto.BookDetailsDTO;
-import io.wkrzywiec.hexagonal.library.domain.book.ports.outgoing.BookDatabase;
-
-import java.util.concurrent.ConcurrentHashMap;
-
-
-public class InMemoryBookDatabase implements BookDatabase {
-
-    ConcurrentHashMap<Long, BookDetailsDTO> books = new ConcurrentHashMap<>();
-
-    @Override
-    public void save(BookDetailsDTO newBookDTO) {
-        Long id = books.size() + 1L;
-        books.put(id, newBookDTO);
-    }
-}

src/test/java/io/wkrzywiec/hexagonal/library/inventory/GetBookDetailsFake.java

@@ -0,0 +1,25 @@
+package io.wkrzywiec.hexagonal.library.inventory;
+
+import io.wkrzywiec.hexagonal.library.TestData;
+import io.wkrzywiec.hexagonal.library.inventory.model.Book;
+import io.wkrzywiec.hexagonal.library.inventory.ports.outgoing.GetBookDetails;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class GetBookDetailsFake implements GetBookDetails {
+
+    private Map<String, Book> books;
+
+    public GetBookDetailsFake() {
+        books = new HashMap<String, Book>();
+        books.put(
+                TestData.homoDeusBookGoogleId(),
+                TestData.homoDeusBook());
+    }
+
+    @Override
+    public Book handle(String bookId) {
+        return books.get(bookId);
+    }
+}

src/test/java/io/wkrzywiec/hexagonal/library/inventory/InMemoryInventoryDatabase.java

@@ -0,0 +1,26 @@
+package io.wkrzywiec.hexagonal.library.inventory;
+
+import io.wkrzywiec.hexagonal.library.inventory.model.Book;
+import io.wkrzywiec.hexagonal.library.inventory.ports.outgoing.InventoryDatabase;
+import org.apache.commons.lang3.reflect.FieldUtils;
+
+import java.util.concurrent.ConcurrentHashMap;
+
+
+public class InMemoryInventoryDatabase implements InventoryDatabase {
+
+    ConcurrentHashMap<Long, Book> books = new ConcurrentHashMap<>();
+
+    @Override
+    public Book save(Book book) {
+        Long id = books.size() + 1L;
+
+        try {
+            FieldUtils.writeField(book, "id", id, true);
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+        books.put(id, book);
+        return book;
+    }
+}

src/test/java/io/wkrzywiec/hexagonal/library/inventory/InvenotryEventPublisherFake.java

@@ -0,0 +1,10 @@
+package io.wkrzywiec.hexagonal.library.inventory;
+
+import io.wkrzywiec.hexagonal.library.inventory.model.NewBookWasAddedEvent;
+import io.wkrzywiec.hexagonal.library.inventory.ports.outgoing.InventoryEventPublisher;
+
+public class InvenotryEventPublisherFake implements InventoryEventPublisher {
+
+    @Override
+    public void publishNewBookWasAddedEvent(NewBookWasAddedEvent event) { }
+}

src/test/java/io/wkrzywiec/hexagonal/library/inventory/InventoryFacadeTest.java

@@ -0,0 +1,46 @@
+package io.wkrzywiec.hexagonal.library.inventory;
+
+import io.wkrzywiec.hexagonal.library.TestData;
+import io.wkrzywiec.hexagonal.library.inventory.model.AddNewBookCommand;
+import io.wkrzywiec.hexagonal.library.inventory.model.Book;
+import io.wkrzywiec.hexagonal.library.inventory.ports.outgoing.GetBookDetails;
+import io.wkrzywiec.hexagonal.library.inventory.ports.outgoing.InventoryEventPublisher;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+
+public class InventoryFacadeTest {
+
+    private GetBookDetails getBookDetails;
+    private InMemoryInventoryDatabase database;
+    private InventoryEventPublisher eventPublisher;
+    private InventoryFacade facade;
+
+    @BeforeEach
+    public void init() {
+        database = new InMemoryInventoryDatabase();
+        getBookDetails = new GetBookDetailsFake();
+        eventPublisher = new InvenotryEventPublisherFake();
+        facade = new InventoryFacade(database, getBookDetails, eventPublisher);
+    }
+
+    @Test
+    @DisplayName("Correctly save a new book in a repository")
+    public void correctlySaveBook(){
+        //given
+        AddNewBookCommand externalBookId = AddNewBookCommand
+                .builder()
+                .googleBookId(TestData.homoDeusBookGoogleId())
+                .build();
+
+        //when
+        facade.handle(externalBookId);
+
+        //then
+        Book actualBook = database.books.get(1L);
+        assertNotNull(actualBook);
+    }
+}

src/test/java/io/wkrzywiec/hexagonal/library/inventory/infrastructure/GoogleBooksAdapterITCase.java

@@ -1,7 +1,7 @@
-package io.wkrzywiec.hexagonal.library.infrastructure.adapter;
+package io.wkrzywiec.hexagonal.library.inventory.infrastructure;
 
 import io.wkrzywiec.hexagonal.library.TestData;
-import io.wkrzywiec.hexagonal.library.domain.book.dto.BookDetailsDTO;
+import io.wkrzywiec.hexagonal.library.inventory.model.Book;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
@@ -32,15 +32,15 @@ public class GoogleBooksAdapterITCase {
     public void givenCorrectBookId_whenGetBookDetails_thenReturnBookDetailsDTO(){
         //given
         String homoDeusResponse = TestData.homoDeusGooleBooksResponse();
-        BookDetailsDTO homoDeusBookDetails = TestData.homoDeusBookDetailsDTO();
+        Book homoDeusBook = TestData.homoDeusBook();
         server.expect(requestTo(
-                "https://www.googleapis.com/books/v1/volumes/" + homoDeusBookDetails.getBookExternalId()))
+                "https://www.googleapis.com/books/v1/volumes/" + TestData.homoDeusBookGoogleId()))
                 .andRespond(withSuccess(homoDeusResponse, MediaType.APPLICATION_JSON));
 
         //when
-        BookDetailsDTO actualBookDetails = googleBooks.handle(homoDeusBookDetails.getBookExternalId());
+        Book actualBook= googleBooks.handle(TestData.homoDeusBookGoogleId());
 
         //then
-        assertEquals(homoDeusBookDetails, actualBookDetails);
+        assertEquals(homoDeusBook, actualBook);
     }
 }

src/test/java/io/wkrzywiec/hexagonal/library/inventory/infrastructure/InventoryDatabaseAdapterITCase.java

@@ -0,0 +1,47 @@
+package io.wkrzywiec.hexagonal.library.inventory.infrastructure;
+
+import io.wkrzywiec.hexagonal.library.TestData;
+import io.wkrzywiec.hexagonal.library.inventory.model.Book;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
+import org.springframework.jdbc.core.JdbcTemplate;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+@DataJpaTest
+public class InventoryDatabaseAdapterITCase {
+
+    @Autowired
+    private BookRepository bookRepository;
+
+    @Autowired
+    private JdbcTemplate jdbcTemplate;
+
+    private InventoryDatabaseAdapter database;
+
+    @BeforeEach
+    public void init() {
+        database = new InventoryDatabaseAdapter(bookRepository);
+    }
+
+    @Test
+    @DisplayName("Save new book in database")
+    public void givenBook_whenSaveIt_thenBookIsSaved() {
+        //given
+        Book homoDeusBook = TestData.homoDeusBook();
+
+        //when
+        Book savedBook = database.save(homoDeusBook);
+
+        //then
+        Long savedBookId = jdbcTemplate.queryForObject(
+                "SELECT id FROM book WHERE id = ?",
+                Long.class,
+                savedBook.getIdAsLong());
+
+        assertEquals(savedBook.getIdAsLong(), savedBookId);
+    }
+}

src/test/java/io/wkrzywiec/hexagonal/library/inventory/model/IsbnTest.java

@@ -0,0 +1,40 @@
+package io.wkrzywiec.hexagonal.library.inventory.model;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class IsbnTest {
+
+    @Test
+    @DisplayName("ISBN-10 is created correctly")
+    public void shouldCreateCorrectISBN10(){
+        assertEquals("1473545374", new Isbn10("1473545374").getAsString());
+    }
+
+    @Test
+    @DisplayName("ISBN-10 is not created")
+    public void shouldNotCreateCorrectISBN10(){
+        assertThrows(
+                IllegalArgumentException.class,
+                () -> new Isbn10("9781473545373").getAsString()
+        );
+    }
+
+    @Test
+    @DisplayName("ISBN-13 is created correctly")
+    public void shouldCreateCorrectISBN13(){
+        assertEquals("9781473545373", new Isbn13("9781473545373").getAsString());
+    }
+
+    @Test
+    @DisplayName("ISBN-13 is not created")
+    public void shouldNotCreateCorrectISBN13(){
+        assertThrows(
+                IllegalArgumentException.class,
+                () -> new Isbn13("1473545374").getAsString()
+        );
+    }
+}