return auto generated ids

persistence-modules/java-jpa-3/pom.xml

@@ -68,6 +68,12 @@
             <version>${assertj.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>${junit.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>

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

@@ -0,0 +1,41 @@
+package com.baeldung.jpa.IdGeneration;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+
+@Entity
+public class User {
+
+    @Id
+//    @GeneratedValue(strategy = GenerationType.SEQUENCE)
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private long id;
+    private String username;
+    private String password;
+
+    public long getId() {
+        return id;
+    }
+
+    public void setId(long id) {
+        this.id = id;
+    }
+
+    public String getUsername() {
+        return username;
+    }
+
+    public void setUsername(String username) {
+        this.username = username;
+    }
+
+    public String getPassword() {
+        return password;
+    }
+
+    public void setPassword(String password) {
+        this.password = password;
+    }
+}

persistence-modules/java-jpa-3/src/main/java/com/baeldung/jpa/IdGeneration/UserService.java

@@ -0,0 +1,19 @@
+package com.baeldung.jpa.IdGeneration;
+
+import javax.persistence.EntityManager;
+import javax.transaction.Transactional;
+
+public class UserService {
+
+    EntityManager entityManager;
+
+    public UserService(EntityManager entityManager) {
+        this.entityManager = entityManager;
+    }
+
+    @Transactional
+    public long saveUser(User user){
+        entityManager.persist(user);
+        return user.getId();
+    }
+}

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

@@ -97,4 +97,20 @@
             <property name="hibernate.temp.use_jdbc_metadata_defaults" value="false"/>
         </properties>
     </persistence-unit>
+
+    <persistence-unit name="jpa-h2-id-generation">
+        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
+        <class>com.baeldung.jpa.IdGeneration.User</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:idGen"/>
+            <property name="javax.persistence.jdbc.user" value="sa"/>
+            <property name="javax.persistence.jdbc.password" value=""/>
+            <property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"/>
+            <property name="hibernate.hbm2ddl.auto" value="create-drop"/>
+            <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/IdGeneration/IdGenerationIntegrationTest.java

@@ -0,0 +1,47 @@
+package com.baeldung.jpa.IdGeneration;
+
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import javax.persistence.EntityManager;
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.Persistence;
+import java.util.UUID;
+
+public class IdGenerationIntegrationTest {
+
+    private static EntityManager entityManager;
+    private static UserService service;
+
+    @BeforeClass
+    public static void setup() {
+        EntityManagerFactory factory = Persistence.createEntityManagerFactory("jpa-h2-id-generation");
+        entityManager = factory.createEntityManager();
+        service = new UserService(entityManager);
+    }
+
+    @Test
+    public void whenNewUserIsPersisted_thenEntityHasNoId() {
+        User user = new User();
+        user.setUsername("test");
+        user.setPassword(UUID.randomUUID().toString());
+
+        long index = service.saveUser(user);
+        Assert.assertEquals(0L, index);
+    }
+
+    @Test
+    public void whenTransactionIsControlled_thenEntityHasId() {
+        User user = new User();
+        user.setUsername("test");
+        user.setPassword(UUID.randomUUID().toString());
+
+        entityManager.getTransaction().begin();
+        long index = service.saveUser(user);
+        entityManager.getTransaction().commit();
+
+        Assert.assertEquals(2L, index);
+    }
+
+}