有没有一种方法可以将分离的对象传递给JPA persist？（已分离的实体传递到持久）

Question

我有两个实体:account和accountRole。

public class Account {
   private AccountRole accountRole;

   @ManyToOne(cascade = CascadeType.PERSIST, fetch = FetchType.EAGER)
   public AccountRole getAccountRole() {
      return accountRole;
   }

.

public class AccountRole {
    private Collection<Account> accounts = new ArrayList<Account>();

    @OneToMany(mappedBy = "accountRole", fetch = FetchType.EAGER)
    public Collection<Account> getAccounts() {
         return accounts;
    }

AccountRole role = accountService.getRoleFromDatabase(AccountRoles.ROLE_USER);
account.setAccountRole(role);

//setting both ways, as suggested
public void setAccountRole(AccountRole accountRole) {
    accountRole.addAccount(this);
    this.accountRole = accountRole;
}

entityManager.persist(account); // finally in my DAO

 org.hibernate.PersistentObjectException: detached entity passed to persist: foo.bar.pojo.AccountRole

Answer 1

只需替换

entityManager.persist(account);

与：

entityManager.merge(account);

并允许合并级联：

@ManyToOne(cascade = { CascadeType.PERSIST, CascadeType.MERGE }, fetch = FetchType.EAGER)
public AccountRole getAccountRole() {
    return accountRole;
}

如果您的实体是新的，它与persist（）相同。但是如果你的实体已经存在，它会更新它。