你每次訪問你的數據庫時都需要創建EntityManager（）嗎？

Question

如果您在行使CRUD方法做你必須做這個（交易類型：RESOURCE_LOCAL沒有JTA）

@PersistenceUnit(unitName="mongo") 
EntityManagerFactory emf; 

EntityManager em; 


@Inject 
private SomeObj injectableObj; 

public void create() 
{ 
    em = emf.createEntityManager(); <---- here 
    SomeObj obj = new SomeObj(); 
    em.persist(obj); 
} 

public void read() 
{ 
    em = emf.createEntityManager(); <---- here 
    Query query = em.createQuery("Select s from SomeObj s"); 

} 

public void update() 
{ 
    em = emf.createEntityManager(); <---- here 
    SomeObj s = em.find(SomeObj.class, injectableObj.getId()); 
    s.setSomeObj(injectableObj.getSomeObj()); 

} 

public void delete() 
{ 

    em = emf.createEntityManager(); <---- here 
    SomeObj s = em.find(SomeObj.class, injectableObj.getId()); 
    em.remove(s); 
} 

問：反正是有注入的EntityManager？

Answer 1

也許嘗試在這裏尋找exemples：

Injections EntityManager

我更喜歡使用：通過注射@PersistenceContext

Answer 2

您可以使用注射。我使用它是這樣的：

@PersistenceContext(unitName = "some_jndi_name") 
private EntityManager em;