spring data jpa : @EntityGraph

spring-data-jpa/src/main/java/com/example/springdatajpa/entity/Member.java

@@ -12,6 +12,7 @@ import javax.persistence.*;
         name="Member.findByUsername",
         query="select m from Member m where m.username = :username"
 )
+@NamedEntityGraph(name = "Member.all", attributeNodes = @NamedAttributeNode("team"))
 public class Member {
 
     @Id @GeneratedValue

spring-data-jpa/src/main/java/com/example/springdatajpa/repository/MemberRepository.java

@@ -5,6 +5,7 @@ import com.example.springdatajpa.entity.Member;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.domain.Slice;
+import org.springframework.data.jpa.repository.EntityGraph;
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.data.jpa.repository.Modifying;
 import org.springframework.data.jpa.repository.Query;
@@ -47,4 +48,19 @@ public interface MemberRepository extends JpaRepository<Member, Long> {
     @Modifying
     @Query("update Member m set m.age = m.age + 1 where m.age >= :age")
     int bulkAgePlus(@Param("age") int age);
+
+    @Query("select m from Member m left join fetch m.team")
+    List<Member> findMemberFetchJoin();
+
+    @Override
+//    @EntityGraph(attributePaths = {"team"})
+    List<Member> findAll();
+
+    @EntityGraph(attributePaths = {"team"})
+    @Query("select m from Member m")
+    List<Member> findMemberEntityGraph();
+
+//    @EntityGraph(attributePaths = {"team"})
+    @EntityGraph("Member.all")
+    List<Member> findEntityGraphByUsername(@Param("username") String username);
 }

spring-data-jpa/src/test/java/com/example/springdatajpa/repository/MemberRepositoryTest.java

@@ -243,5 +243,41 @@ public class MemberRepositoryTest {
         // then
         assertEquals(3, resultCount);
     }
+
+    @Test
+    void findMemberLazy() {
+        // given
+        // member1 -> teamA
+        // member2 -> teamB
+
+        Team teamA = new Team("teamA");
+        Team teamB = new Team("teamB");
+        teamRepository.save(teamA);
+        teamRepository.save(teamB);
+        Member member1 = new Member("member1", 10, teamA);
+        Member member2 = new Member("member2", 10, teamB);
+        memberRepository.save(member1);
+        memberRepository.save(member2);
+
+        em.flush();
+        em.clear();
+
+        // when
+        List<Member> members = memberRepository.findAll();
+        members.forEach(member -> {
+            System.out.println("member.getUsername() = " + member.getUsername());
+            System.out.println("member.getTeam().getClass() = " + member.getTeam().getClass()); // Lazy 로딩 이므로 프록시 객체
+            System.out.println("member.getTeam().getName() = " + member.getTeam().getName()); // 이때 실제로 team 데이터 조회 ( N + 1 문제 발생 )
+        });
+
+        // fetch join 으로 해결 -> 한 번에 team 데이터도 모두 조회
+        // @EntityGraph(attributePaths = {"team"}) 사용 가능
+        List<Member> memberFetchJoin = memberRepository.findMemberFetchJoin();
+        memberFetchJoin.forEach(member -> {
+            System.out.println("member.getUsername() = " + member.getUsername());
+            System.out.println("member.getTeam().getClass() = " + member.getTeam().getClass());
+            System.out.println("member.getTeam().getName() = " + member.getTeam().getName()); // fetch join
+        });
+    }
 }