java – 使用Spring的JPA的手动事务服务和DAO层

我正在使用JPA和Spring.如果我让Spring处理事务,那么假设EntityManager已正确注入DAO,这就是我的服务层的样子：

MyService {

   @Transactional
   public void myMethod() {
       myDaoA.doSomething();
       myDaoB.doSomething();
    }
}

但是,如果我要手动执行事务,我必须确保将EntityManager的实例传递到事务中的每个DAO中.任何想法如何更好地重构？我很难做新的MyDaoA(em)或将em传递给每个DAO方法,如doSomething(em).

MyService {

   private EntityManagerFactory emf;

   public void myMethod() {
       EntityManager em = emf.createEntityManager();
       EntityTransaction tx = em.getTransaction();
       MyDaoA myDaoA = new MyDaoA(em);
       MyDaoB myDaoB = new MyDaoB(em);
       try {
           tx.begin();
           myDaoA.doSomething();
           myDaoB.doSomething();
           tx.commit();
       } catch(Exception e) {
           tx.rollback();
       }
    }
}

最佳答案

However,if I were to do transactions
manually,I have to make sure to pass
that instance of EntityManager into
each of the DAOs within a transaction.

这是你错了.来自Spring Reference,JPA section：

The main problem with such a DAO is
that it always creates a new
EntityManager through the factory. You
can avoid this by requesting a
transactional EntityManager (also
called “shared EntityManager” because
it is a shared,thread-safe proxy for
the actual transactional
EntityManager) to be injected instead
of the factory:

public class ProductDaoImpl implements ProductDao {

    @PersistenceContext
    private EntityManager em;

    public Collection loadProductsByCategory(String category) {
       Query query = em.createquery(
                        "from Product as p where p.category = :category");
       query.setParameter("category",category);
       return query.getResultList(); 
    }
}

The @PersistenceContext annotation has
an optional attribute type,which
defaults to
PersistenceContextType.TRANSACTION.
This default is what you need to
receive a shared EntityManager proxy.