JPA Entity Graph.

persistence-modules/java-jpa/src/main/java/com/baeldung/jpa/entitygraph/MainApp.java

@@ -0,0 +1,26 @@
+package com.baeldung.jpa.entitygraph;
+
+import com.baeldung.jpa.entitygraph.model.Post;
+import com.baeldung.jpa.entitygraph.repo.PostRepository;
+
+public class MainApp {
+
+    public static void main(String... args) {
+        Long postId = 1L;
+        Post post = null;
+        PostRepository postRepository = new PostRepository();
+
+        //Using EntityManager.find().
+        post = postRepository.find(postId);
+        post = postRepository.findWithEntityGraph(postId);
+        post = postRepository.findWithEntityGraph2(postId);
+
+        //Using JPQL: Query and TypedQuery
+        post = postRepository.findUsingJpql(postId);
+
+        //Using Criteria API
+        post = postRepository.findUsingCriteria(postId);
+
+        postRepository.clean();
+    }
+}

persistence-modules/java-jpa/src/main/java/com/baeldung/jpa/entitygraph/model/Comment.java

@@ -0,0 +1,63 @@
+package com.baeldung.jpa.entitygraph.model;
+
+import javax.persistence.*;
+
+@Entity
+public class Comment {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    private String reply;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn
+    private Post post;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn
+    private User user;
+    //...
+
+    public Comment() {
+    }
+
+    public Comment(String reply, Post post, User user) {
+        this.reply = reply;
+        this.post = post;
+        this.user = user;
+    }
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getReply() {
+        return reply;
+    }
+
+    public void setReply(String reply) {
+        this.reply = reply;
+    }
+
+    public Post getPost() {
+        return post;
+    }
+
+    public void setPost(Post post) {
+        this.post = post;
+    }
+
+    public User getUser() {
+        return user;
+    }
+
+    public void setUser(User user) {
+        this.user = user;
+    }
+}

persistence-modules/java-jpa/src/main/java/com/baeldung/jpa/entitygraph/model/Post.java

@@ -0,0 +1,86 @@
+package com.baeldung.jpa.entitygraph.model;
+
+import javax.persistence.*;
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.List;
+
+@NamedEntityGraph(
+        name = "post-entity-graph",
+        attributeNodes = {
+                @NamedAttributeNode("subject"),
+                @NamedAttributeNode("user"),
+                @NamedAttributeNode("comments"),
+        }
+)
+@NamedEntityGraph(
+        name = "post-entity-graph-with-comment-users",
+        attributeNodes = {
+                @NamedAttributeNode("subject"),
+                @NamedAttributeNode("user"),
+                @NamedAttributeNode(value = "comments", subgraph = "comments-subgraph"),
+        },
+        subgraphs = {
+                @NamedSubgraph(
+                        name = "comments-subgraph",
+                        attributeNodes = {
+                                @NamedAttributeNode("user")
+                        }
+                )
+        }
+)
+@Entity
+public class Post {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+    private String subject;
+    @OneToMany(mappedBy = "post")
+    private List<Comment> comments = new ArrayList<>();
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn
+    private User user;
+    //...
+
+    public Post() {
+    }
+
+    public Post(String subject, User user) {
+        this.subject = subject;
+        this.user = user;
+    }
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getSubject() {
+        return subject;
+    }
+
+    public void setSubject(String subject) {
+        this.subject = subject;
+    }
+
+    public List<Comment> getComments() {
+        return comments;
+    }
+
+    public void setComments(List<Comment> comments) {
+        this.comments = comments;
+    }
+
+    public User getUser() {
+        return user;
+    }
+
+    public void setUser(User user) {
+        this.user = user;
+    }
+}

persistence-modules/java-jpa/src/main/java/com/baeldung/jpa/entitygraph/model/User.java

@@ -0,0 +1,48 @@
+package com.baeldung.jpa.entitygraph.model;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+
+@Entity
+public class User {
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+    private String name;
+    private String email;
+
+    //...
+
+    public User() {
+    }
+
+    public User(String email) {
+        this.email = email;
+    }
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+}

persistence-modules/java-jpa/src/main/java/com/baeldung/jpa/entitygraph/repo/PostRepository.java

@@ -0,0 +1,93 @@
+package com.baeldung.jpa.entitygraph.repo;
+
+import com.baeldung.jpa.entitygraph.model.Post;
+
+import javax.persistence.*;
+import javax.persistence.criteria.CriteriaBuilder;
+import javax.persistence.criteria.CriteriaQuery;
+import javax.persistence.criteria.Root;
+import java.util.HashMap;
+import java.util.Map;
+
+public class PostRepository {
+    private EntityManagerFactory emf = null;
+
+
+    public PostRepository() {
+        Map properties = new HashMap();
+        properties.put("hibernate.show_sql", "true");
+        properties.put("hibernate.format_sql", "true");
+        emf = Persistence.createEntityManagerFactory("entity-graph-pu", properties);
+    }
+
+    public Post find(Long id) {
+        EntityManager entityManager = emf.createEntityManager();
+
+        Post post = entityManager.find(Post.class, id);
+
+        entityManager.close();
+        return post;
+    }
+
+    public Post findWithEntityGraph(Long id) {
+        EntityManager entityManager = emf.createEntityManager();
+
+        EntityGraph entityGraph = entityManager.getEntityGraph("post-entity-graph");
+        Map<String, Object> properties = new HashMap<>();
+        properties.put("javax.persistence.fetchgraph", entityGraph);
+        Post post = entityManager.find(Post.class, id, properties);
+
+        entityManager.close();
+        return post;
+    }
+
+    public Post findWithEntityGraph2(Long id) {
+        EntityManager entityManager = emf.createEntityManager();
+
+        EntityGraph<Post> entityGraph = entityManager.createEntityGraph(Post.class);
+        entityGraph.addAttributeNodes("subject");
+        entityGraph.addAttributeNodes("user");
+        entityGraph.addSubgraph("comments")
+                .addAttributeNodes("user");
+
+        Map<String, Object> properties = new HashMap<>();
+        properties.put("javax.persistence.fetchgraph", entityGraph);
+        Post post = entityManager.find(Post.class, id, properties);
+
+        entityManager.close();
+        return post;
+    }
+
+    public Post findUsingJpql(Long id) {
+        EntityManager entityManager = emf.createEntityManager();
+
+        EntityGraph entityGraph = entityManager.getEntityGraph("post-entity-graph-with-comment-users");
+        Post post = entityManager.createQuery("Select p from Post p where p.id=:id", Post.class)
+                .setParameter("id", id)
+                .setHint("javax.persistence.fetchgraph", entityGraph)
+                .getSingleResult();
+
+        entityManager.close();
+        return post;
+    }
+
+    public Post findUsingCriteria(Long id) {
+        EntityManager entityManager = emf.createEntityManager();
+
+        EntityGraph entityGraph = entityManager.getEntityGraph("post-entity-graph-with-comment-users");
+        CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
+        CriteriaQuery<Post> criteriaQuery = criteriaBuilder.createQuery(Post.class);
+        Root<Post> root = criteriaQuery.from(Post.class);
+        criteriaQuery.where(criteriaBuilder.equal(root.<Long>get("id"), id));
+        TypedQuery<Post> typedQuery = entityManager.createQuery(criteriaQuery);
+        typedQuery.setHint("javax.persistence.loadgraph", entityGraph);
+        Post post = typedQuery.getSingleResult();
+
+        entityManager.close();
+        return post;
+    }
+
+    public void clean() {
+        emf.close();
+    }
+}

persistence-modules/java-jpa/src/main/resources/META-INF/persistence.xml

@@ -9,12 +9,12 @@
         <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
         <class>com.baeldung.sqlresultsetmapping.ScheduledDay</class>
         <properties>
-            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver" />
+            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver"/>
             <property name="javax.persistence.jdbc.url"
-                      value="jdbc:h2:mem:test;INIT=RUNSCRIPT FROM 'classpath:database.sql'" />
+                      value="jdbc:h2:mem:test;INIT=RUNSCRIPT FROM 'classpath:database.sql'"/>
-            <property name="javax.persistence.jdbc.user" value="sa" />
+            <property name="javax.persistence.jdbc.user" value="sa"/>
-            <property name="javax.persistence.jdbc.password" value="" />
+            <property name="javax.persistence.jdbc.password" value=""/>
-            <property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect" />
+            <property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"/>
             <!--<property name="hibernate.hbm2ddl.auto" value="create-drop" />-->
             <property name="show_sql" value="true"/>
             <property name="hibernate.temp.use_jdbc_metadata_defaults" value="false"/>
@@ -25,28 +25,45 @@
         <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
         <class>com.baeldung.jpa.stringcast.Message</class>
         <properties>
-            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver" />
+            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver"/>
-            <property name="javax.persistence.jdbc.url" value="jdbc:h2:mem:test" />
+            <property name="javax.persistence.jdbc.url" value="jdbc:h2:mem:test"/>
-            <property name="javax.persistence.jdbc.user" value="sa" />
+            <property name="javax.persistence.jdbc.user" value="sa"/>
-            <property name="javax.persistence.jdbc.password" value="" />
+            <property name="javax.persistence.jdbc.password" value=""/>
-            <property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect" />
+            <property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"/>
-            <property name="hibernate.hbm2ddl.auto" value="create-drop" />
+            <property name="hibernate.hbm2ddl.auto" value="create-drop"/>
             <property name="show_sql" value="true"/>
             <property name="hibernate.temp.use_jdbc_metadata_defaults" value="false"/>
         </properties>
     </persistence-unit>
-    
+
     <persistence-unit name="jpa-db">
         <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
         <class>com.baeldung.jpa.model.Car</class>
         <properties>
-            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
+            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
-            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://127.0.0.1:3306/baeldung" />
+            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://127.0.0.1:3306/baeldung"/>
-            <property name="javax.persistence.jdbc.user" value="baeldung" />
+            <property name="javax.persistence.jdbc.user" value="baeldung"/>
-            <property name="javax.persistence.jdbc.password" value="YourPassword" />
+            <property name="javax.persistence.jdbc.password" value="YourPassword"/>
-            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect" />
+            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>
-            <property name="hibernate.show_sql" value="true" />
+            <property name="hibernate.show_sql" value="true"/>
         </properties>
     </persistence-unit>
-	
+
+    <persistence-unit name="entity-graph-pu" transaction-type="RESOURCE_LOCAL">
+        <class>com.baeldung.jpa.entitygraph.model.Post</class>
+        <class>com.baeldung.jpa.entitygraph.model.User</class>
+        <class>com.baeldung.jpa.entitygraph.model.Comment</class>
+        <exclude-unlisted-classes>true</exclude-unlisted-classes>
+        <properties>
+
+            <!--H2-->
+            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver"/>
+            <property name="javax.persistence.jdbc.url"
+                      value="jdbc:h2:mem:entitygraphdb;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE"/>
+
+            <property name="javax.persistence.schema-generation.database.action" value="drop-and-create"/>
+            <property name="javax.persistence.sql-load-script-source" value="data-init.sql"/>
+        </properties>
+    </persistence-unit>
+
 </persistence>

persistence-modules/java-jpa/src/main/resources/data-init.sql

@@ -0,0 +1,8 @@
+INSERT INTO `USER` (`ID`,`NAME`,`EMAIL`) VALUES (1,'user1','user1@test.com');
+INSERT INTO `USER` (`ID`,`NAME`,`EMAIL`) VALUES (2,'user2','user2@test.com');
+INSERT INTO `USER` (`ID`,`NAME`,`EMAIL`) VALUES (3,'user3','user3@test.com');
+
+INSERT INTO `POST` (`ID`,`SUBJECT`,`USER_ID`) VALUES (1,'JPA Entity Graph In Action',1);
+
+INSERT INTO `COMMENT` (`ID`,`REPLY`,`POST_ID`,`USER_ID`) VALUES (1,'Nice !!',1,2);
+INSERT INTO `COMMENT` (`ID`,`REPLY`,`POST_ID`,`USER_ID`) VALUES (2,'Cool !!',1,3);

persistence-modules/java-jpa/src/test/java/com/baeldung/jpa/entitygraph/repo/PostRepositoryTest.java

@@ -0,0 +1,68 @@
+package com.baeldung.jpa.entitygraph.repo;
+
+import com.baeldung.jpa.entitygraph.model.Comment;
+import com.baeldung.jpa.entitygraph.model.Post;
+import com.baeldung.jpa.entitygraph.model.User;
+import org.hibernate.LazyInitializationException;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class PostRepositoryTest {
+
+    private static PostRepository postRepository = null;
+
+    @BeforeClass
+    public static void once() {
+        postRepository = new PostRepository();
+    }
+
+    @Test(expected = LazyInitializationException.class)
+    public void find() {
+        Post post = postRepository.find(1L);
+        assertNotNull(post.getUser());
+        String email = post.getUser().getEmail();
+        assertNull(email);
+    }
+
+    @Test
+    public void findWithEntityGraph() {
+        Post post = postRepository.findWithEntityGraph(1L);
+        assertNotNull(post.getUser());
+        String email = post.getUser().getEmail();
+        assertNotNull(email);
+    }
+
+    @Test(expected = LazyInitializationException.class)
+    public void findWithEntityGraph_Comment_Without_User() {
+        Post post = postRepository.findWithEntityGraph(1L);
+        assertNotNull(post.getUser());
+        String email = post.getUser().getEmail();
+        assertNotNull(email);
+        assertNotNull(post.getComments());
+        assertEquals(post.getComments().size(), 2);
+        Comment comment = post.getComments().get(0);
+        assertNotNull(comment);
+        User user = comment.getUser();
+        user.getEmail();
+    }
+
+    @Test
+    public void findWithEntityGraph2_Comment_With_User() {
+        Post post = postRepository.findWithEntityGraph2(1L);
+        assertNotNull(post.getComments());
+        assertEquals(post.getComments().size(), 2);
+        Comment comment = post.getComments().get(0);
+        assertNotNull(comment);
+        User user = comment.getUser();
+        assertNotNull(user);
+        assertEquals(user.getEmail(), "user2@test.com");
+    }
+
+    @AfterClass
+    public static void destroy() {
+        postRepository.clean();
+    }
+}