java - JPA如何在双向ManyToOne中保留父级

Question

我有一个与帐户具有双向 ManyToOne 关系的付款实体。

@Table(name="account")
public class Account implements Serializable { 

    //bi-directional many-to-one association to Payment
    @OneToMany(mappedBy="account",fetch=FetchType.EAGER)
    private List<Payment> payments;

@Table(name="payment")
public class Payment implements Serializable { 

    //bi-directional many-to-one association to Account
    @ManyToOne(cascade={CascadeType.MERGE},fetch=FetchType.EAGER)
    @JoinColumn(name="idAcc")
    private Account account;

帐户实体已保留。我在浏览器和数据库中看到了相关信息:

Account [idAcc=475, account=12345678901230, isLock=N, rest=10000.5]

然后我需要保留子实体(付款实体)并同时更改帐户实体(更改帐户休息)。我使用这个代码。

    public class GenericDaoImpl<T> implements GenericDao<T> {

        protected Class<T> type; 
        protected EntityManagerFactory emf = null;

        public GenericDaoImpl(Class<T> type, EntityManagerFactory emf) { 
            this.emf = emf;
            this.type = type;       
        } 

        @Override
        public void create(T entity) throws Exception { 
            EntityManager em = null; 
            try { 
                em = getEntityManager();
                em.getTransaction().begin();  
                em.persist(entity); 
                em.getTransaction().commit(); 
            } 
...
@Override
    public T findById(String id) {
         EntityManager em = getEntityManager();
            try {
                Query query = em.createNamedQuery(type.getSimpleName()+".findByName");
                query.setParameter("id", id);
                return (T)query.getSingleResult();
            } finally {
                em.close();
            }
    }

还有

daoPayments = new GenericDaoImpl(Payment.class,factory); 
            Payment payment = null;
                try {
                    payment = new Payment();
                    payment.setDescription("Shop 'Pirasmani'");
                    payment.setSumm(50.25);
                        Account account = (Account)daoAccount.findById(listAccount.get(0).getIdAcc());
                        account.setRest(account.getRest()-payment.getSumm());
                        payment.setAccount(account);
                        account.getPayments().add(payment);

                    daoPayments.create(payment);
                    //print result 
                    Payment paymentMerged = (Payment)daoPayments.read(payment);
                    out.println(paymentMerged.toString()+"<br>"); 

然后我在浏览器中看到帐户休息已更改:

Payment [idPmnt=91, description=Shop 'Pirasmani', summ=50.25, account=Account [idAcc=475, account=12345678901230, isLock=N, rest=9950.25]]

但是在数据库中帐户剩余没有任何变化。它的钢=10000.5。我究竟做错了什么？谢谢。

Answer 1

您不应在 DAO 方法中启动和停止事务。最后一部分中的所有代码都应该位于单个事务中，这将允许您

• 处理附加实体，并自动保留对帐户所做的所有更改
• 删除关联上不必要的 cascade={CascadeType.MERGE}
• 让数据库保持一致的状态，而不是像现在一样处于付款已创建但其余部分尚未减少的状态(这就是我们首先使用交易的原因)。

也就是说，您坚持付款。为什么这会导致其帐户发生任何修改？您拥有的唯一级联是 MERGE，并且您没有在代码中进行任何合并。