BAEL-4887: fetching multiple entities in JPA query (#10803)

persistence-modules/java-jpa-3/src/main/java/com/baeldung/jpa/returnmultipleentities/Channel.java

@@ -0,0 +1,43 @@
+package com.baeldung.jpa.returnmultipleentities;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+import java.util.Objects;
+
+@Entity
+public class Channel {
+    @Id
+    @GeneratedValue(strategy = GenerationType.AUTO)
+    private Long id;
+
+    private String code;
+
+    private Long subscriptionId;
+
+    public void setCode(String code) {
+        this.code = code;
+    }
+
+    public String getCode() {
+        return code;
+    }
+
+    public void setSubscriptionId(Long subscriptionId) {
+        this.subscriptionId = subscriptionId;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        Channel channel = (Channel) o;
+        return Objects.equals(id, channel.id) && Objects.equals(code, channel.code) && Objects.equals(subscriptionId, channel.subscriptionId);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(id, code, subscriptionId);
+    }
+}

persistence-modules/java-jpa-3/src/main/java/com/baeldung/jpa/returnmultipleentities/ReportRepository.java

@@ -0,0 +1,23 @@
+package com.baeldung.jpa.returnmultipleentities;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.Persistence;
+import javax.persistence.Query;
+import java.util.List;
+
+public class ReportRepository {
+    private final EntityManagerFactory emf;
+
+    public ReportRepository() {
+        emf = Persistence.createEntityManagerFactory("jpa-h2-return-multiple-entities");
+    }
+
+    public List<Object[]> find(String email) {
+        EntityManager entityManager = emf.createEntityManager();
+        Query query = entityManager.createQuery("SELECT c, s, u FROM  Channel c, Subscription s, User u WHERE c.subscriptionId = s.id AND s.id = u.subscriptionId AND u.email=:email");
+        query.setParameter("email", email);
+
+        return query.getResultList();
+    }
+}

persistence-modules/java-jpa-3/src/main/java/com/baeldung/jpa/returnmultipleentities/Subscription.java

@@ -0,0 +1,41 @@
+package com.baeldung.jpa.returnmultipleentities;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+import java.util.Objects;
+
+@Entity
+public class Subscription {
+    @Id
+    @GeneratedValue(strategy = GenerationType.AUTO)
+    private Long id;
+
+    private String code;
+
+    public void setCode(String code) {
+        this.code = code;
+    }
+
+    public String getCode() {
+        return code;
+    }
+
+    public Long getId() {
+        return id;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        Subscription subscription = (Subscription) o;
+        return Objects.equals(id, subscription.id) && Objects.equals(code, subscription.code);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(id, code);
+    }
+}

persistence-modules/java-jpa-3/src/main/java/com/baeldung/jpa/returnmultipleentities/User.java

@@ -0,0 +1,29 @@
+package com.baeldung.jpa.returnmultipleentities;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+
+@Entity
+public class User {
+    @Id
+    @GeneratedValue(strategy = GenerationType.AUTO)
+    private Long id;
+
+    private String email;
+
+    private Long subscriptionId;
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+
+    public void setSubscriptionId(Long subscriptionId) {
+        this.subscriptionId = subscriptionId;
+    }
+}

persistence-modules/java-jpa-3/src/main/resources/META-INF/persistence.xml

@@ -113,4 +113,24 @@
             <property name="hibernate.temp.use_jdbc_metadata_defaults" value="false"/>
         </properties>
     </persistence-unit>
+    <persistence-unit name="jpa-h2-return-multiple-entities">
+        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
+        <class>com.baeldung.jpa.returnmultipleentities.Channel</class>
+        <class>com.baeldung.jpa.returnmultipleentities.Subscription</class>
+        <class>com.baeldung.jpa.returnmultipleentities.User</class>
+        <class>com.baeldung.jpa.returnmultipleentities.ReportRepository</class>
+        <exclude-unlisted-classes>true</exclude-unlisted-classes>
+        <properties>
+            <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.user" value="sa"/>
+            <property name="javax.persistence.jdbc.password" value=""/>
+            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver"/>
+            <property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"/>
+            <property name="hibernate.hbm2ddl.auto" value="create-drop"/>
+            <property name="hibernate.show_sql" value="true"/>
+            <property name="hibernate.format_sql" value="true"/>
+            <property name="hibernate.temp.use_jdbc_metadata_defaults" value="false"/>
+        </properties>
+    </persistence-unit>
 </persistence>

persistence-modules/java-jpa-3/src/test/java/com/baeldung/jpa/returnmultipleentities/ReturnMultipleEntitiesIntegrationTest.java

@@ -0,0 +1,84 @@
+package com.baeldung.jpa.returnmultipleentities;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.Persistence;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class ReturnMultipleEntitiesIntegrationTest {
+    private static EntityManagerFactory factory;
+    private static EntityManager entityManager;
+    private ReportRepository reportRepository;
+
+    @Before
+    public void setup() {
+        factory = Persistence.createEntityManagerFactory("jpa-h2-return-multiple-entities");
+        entityManager = factory.createEntityManager();
+        reportRepository = new ReportRepository();
+        populateH2DB();
+    }
+
+    @Test
+    public void whenQueryingForMultipleEntitiesInOneQuery_thenJPAReturnsMultipleEntitiesInCorrectOrder() {
+        List<Object[]> reportDetails = reportRepository.find("user1@gmail.com");
+
+        assertEquals(2, reportDetails.size());
+
+        for (Object[] reportDetail : reportDetails) {
+            assertEquals(3, reportDetail.length);
+
+            Channel channel = (Channel) reportDetail[0];
+            Subscription subscription = (Subscription) reportDetail[1];
+            User user = (User) reportDetail[2];
+
+            assertEquals("single", subscription.getCode());
+            assertEquals("user1@gmail.com", user.getEmail());
+            if (!("eurosport".equals(channel.getCode()) || "hbo".equals(channel.getCode()))) {
+                fail();
+            }
+        }
+    }
+
+    private static void populateH2DB() {
+        entityManager.getTransaction().begin();
+
+        Subscription single = new Subscription();
+        single.setCode("single");
+
+        Subscription family = new Subscription();
+        family.setCode("family");
+
+        entityManager.persist(single);
+        entityManager.persist(family);
+
+        Channel bbc = new Channel();
+        bbc.setCode("bbc");
+        bbc.setSubscriptionId(family.getId());
+
+        Channel eurosport = new Channel();
+        eurosport.setCode("eurosport");
+        eurosport.setSubscriptionId(single.getId());
+
+        Channel hbo = new Channel();
+        hbo.setCode("hbo");
+        hbo.setSubscriptionId(single.getId());
+
+        entityManager.persist(bbc);
+        entityManager.persist(eurosport);
+        entityManager.persist(hbo);
+
+        User user1 = new User();
+        user1.setEmail("user1@gmail.com");
+        user1.setSubscriptionId(single.getId());
+
+        entityManager.persist(user1);
+
+        entityManager.getTransaction().commit();
+    }
+}