我有一个包含多对一关系的jpa持久化对象模型:一个Account有多个transaction。一个事务有一个帐户。
下面是一段代码:
@Entity
public class Transaction {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
@ManyToOne(cascade = {CascadeType.ALL},fetch= FetchType.EAGER)
private Account fromAccount;
....
@Entity
public class Account {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
@OneToMany(cascade = {CascadeType.ALL},fetch= FetchType.EAGER, mappedBy = "fromAccount")
private Set<Transaction> transactions;
我能够创建Account对象，向其添加事务，并正确地持久化Account对象。但是，当我创建一个事务，使用现有的已经持久化的帐户，并持久化的事务，我得到一个异常:
导致:org.hibernate.PersistentObjectException:传递给persist: com.paulsanwald.Account的分离实体
org.hibernate.event.internal.DefaultPersistEventListener.onPersist (DefaultPersistEventListener.java: 141)
因此，我能够持久化一个包含事务的Account，但不能持久化一个具有Account的Transaction。我认为这是因为帐户可能没有附加，但这段代码仍然给了我相同的异常:
if (account.getId()!=null) {
account = entityManager.merge(account);
}
Transaction transaction = new Transaction(account,"other stuff");
// the below fails with a "detached entity" message. why?
entityManager.persist(transaction);
如何正确地保存与已经持久化的帐户对象相关联的事务?
移除子关联级联
因此，您需要删除@CascadeType。这些都来自@ManyToOne协会。子实体不应该级联到父关联。只有父实体应该级联到子实体。
@ManyToOne(fetch= FetchType.LAZY)
注意，我将fetch属性设置为FetchType。LAZY，因为急切抓取对性能非常不利。
设置关联的双方
当你有一个双向关联时，你需要在父实体中使用addChild和removecchild方法来同步双方:
public void addTransaction(Transaction transaction) {
transcations.add(transaction);
transaction.setAccount(this);
}
public void removeTransaction(Transaction transaction) {
transcations.remove(transaction);
transaction.setAccount(null);
}
使用合并是有风险和棘手的，所以在您的情况下，这是一种肮脏的变通方法。您至少需要记住，当您将一个实体对象传递给merge时，它将停止附加到事务，而是返回一个新的、现在已附加的实体。这意味着如果任何人仍然拥有旧的实体对象，那么对它的更改将被无声地忽略并在提交时丢弃。
You are not showing the complete code here, so I cannot double-check your transaction pattern. One way to get to a situation like this is if you don't have a transaction active when executing the merge and persist. In that case persistence provider is expected to open a new transaction for every JPA operation you perform and immediately commit and close it before the call returns. If this is the case, the merge would be run in a first transaction and then after the merge method returns, the transaction is completed and closed and the returned entity is now detached. The persist below it would then open a second transaction, and trying to refer to an entity that is detached, giving an exception. Always wrap your code inside a transaction unless you know very well what you are doing.
使用容器管理的事务，它看起来像这样。注意:这假设方法在会话bean中，并通过本地或远程接口调用。
@TransactionAttribute(TransactionAttributeType.REQUIRED)
public void storeAccount(Account account) {
...
if (account.getId()!=null) {
account = entityManager.merge(account);
}
Transaction transaction = new Transaction(account,"other stuff");
entityManager.persist(account);
}
