JPA Remove/Delete Entity Example

In JPA, to remove an entity, the entity itself must be managed, meaning that it is present in the persistence context. This means that the calling application should have already loaded or accessed the entity and is now issuing a command to remove it. This is not normally a problem given that most often the application will have caused it to become managed as part of the process of determining that this was the object that it wanted to remove.

Using EntityManager.remove()

@ContextConfiguration(locations = "classpath:application-context-test.xml")
@RunWith(SpringJUnit4ClassRunner.class)
public class TestRemoveEntity {
	
	@PersistenceContext
    private EntityManager manager;
	
	private static Integer departmentId;
	
	@Before
	public void setupData() 
	{
		DepartmentEntity department = new DepartmentEntity("Information Technology");
		manager.persist(department);
		departmentId = department.getId();
	}
	
	@Test
	@Transactional
	@Rollback(true)
	public void testRemoveDepartment()
	{
		//Find managed Entity reference
		DepartmentEntity department = manager.find(DepartmentEntity.class, departmentId);
		
		//Call remove method to remove the entity
		if(department != null){
			manager.remove(department);
		}
		
		List<DepartmentEntity> departments = manager.createQuery("Select a From DepartmentEntity a", 
		DepartmentEntity.class).getResultList();
		
		Assert.assertEquals(0, departments.size());
	}
}

In this example, we are first finding the entity using the find() call, which returns a managed instance of DepartmentEntity, and then removing the entity using the remove() call on the entity manager.

This method will ensure that the department with the given id, provided the id is not null, is removed from the database. It will return successfully whether the department exists or not.

Remove a row using JPQL Query

Another way to remove entity is using JPQL (Java Persistence Query Language) in below manner.

//Delete entity using JP QL
Query query = manager.createNativeQuery("DELETE FROM DEPARTMENT WHERE ID = " + departmentId);
query.executeUpdate();

In fact, in this way you remove multiple rows in single query, which is not possible using EntityManager.remove() method.

//Delete all rows in single query
Query query = manager.createNativeQuery("DELETE FROM DEPARTMENT");
query.executeUpdate();

Above code is built and tested using sourcecode provided for this tutorial.

Happy Learning !!