#30 jpa basic: jpql - fetch join

hello-jpa/src/main/java/com/hello/jpa/query/FetchJoin.java

@@ -0,0 +1,102 @@
+package com.hello.jpa.query;
+
+import com.hello.jpa.query.entity.Member;
+import com.hello.jpa.query.entity.Team;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.EntityTransaction;
+import javax.persistence.Persistence;
+import java.util.List;
+
+public class FetchJoin {
+
+    public static void main(String[] args) {
+        EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");
+
+        EntityManager em = emf.createEntityManager();
+
+        EntityTransaction tx = em.getTransaction();
+        tx.begin();
+
+        try {
+            Team team = new Team();
+            team.setName("team1");
+            em.persist(team);
+
+            Team team2 = new Team();
+            team2.setName("team2");
+            em.persist(team2);
+
+            Member member = new Member();
+            member.setName("member1");
+            member.setTeam(team);
+            em.persist(member);
+
+            Member member2 = new Member();
+            member2.setName("member2");
+            member2.setTeam(team);
+            em.persist(member2);
+
+            Member member3 = new Member();
+            member3.setName("member3");
+            member3.setTeam(team2);
+            em.persist(member3);
+
+            em.flush();
+            em.clear();
+
+//            List<Member> result = em.createQuery(
+//                            "select m from Member m join fetch m.team",
+//                            Member.class
+//                    )
+//                    .getResultList();
+//
+//            result.forEach(m -> {
+//                System.out.println("m.getName() = " + m.getName() + ", " + m.getTeam().getName());
+//            });
+//
+//            List<Team> result2 = em.createQuery(
+//                            "select t from Team t join fetch t.members",
+//                            Team.class
+//                    )
+//                    .getResultList();
+//
+//            result2.forEach(t -> {
+//                System.out.println("team = " + t.getName() + ", members = " + t.getMembers().size());
+//            });
+//
+//            List<Team> result3 = em.createQuery(
+//                            "select distinct t from Team t join fetch t.members",
+//                            Team.class
+//                    )
+//                    .getResultList();
+//
+//            result3.forEach(t -> {
+//                System.out.println("team = " + t.getName() + ", members = " + t.getMembers().size());
+//            });
+
+            List<Team> result4 = em.createQuery(
+                            "select t from Team t",
+                            Team.class
+                    )
+                    .setFirstResult(0)
+                    .setMaxResults(2)
+                    .getResultList();
+
+            result4.forEach(t -> {
+                System.out.println("team = " + t.getName() + ", members = " + t.getMembers().size());
+                t.getMembers().forEach(System.out::println);
+            });
+
+            tx.commit();
+        } catch (Exception e) {
+            e.printStackTrace();
+            tx.rollback();
+        } finally {
+            em.close();
+        }
+
+        emf.close();
+    }
+}

hello-jpa/src/main/java/com/hello/jpa/query/entity/Team.java

@@ -1,5 +1,7 @@
 package com.hello.jpa.query.entity;
 
+import org.hibernate.annotations.BatchSize;
+
 import javax.persistence.Entity;
 import javax.persistence.GeneratedValue;
 import javax.persistence.Id;
@@ -15,6 +17,7 @@ public class Team {
     private Long id;
     private String name;
 
+    @BatchSize(size = 100)
     @OneToMany(mappedBy = "team")
     private List<Member> members = new ArrayList<>();
 

hello-jpa/src/main/resources/META-INF/persistence.xml

@@ -56,6 +56,7 @@
             <property name="hibernate.format_sql" value="true"/>
             <property name="hibernate.use_sql_comments" value="true"/>
             <property name="hibernate.hbm2ddl.auto" value="create" />
+            <property name="hibernate.default_batch_fetch_size" value="100" />
         </properties>
     </persistence-unit>
 </persistence>