从google app engine中的集合中删除不会被持久化

我在中看到了类似的问题 Problems while saving a pre-persisted object in Google App Engine (Java) 实际上,我并没有在持久性管理器上调用close()。但是,我现在正在调用Close,但是我的对象更新没有被持久化。具体来说,我想从集合中删除一个元素,并保存较小的集合。下面是与持久性管理器相关的代码,它不会引发异常,但不会保存我的数据:

    UserService userService = UserServiceFactory.getUserService();
    User user = userService.getCurrentUser();

    PersistenceManager pm = PMF.get().getPersistenceManager();
    UserProfileInfo userProfile = pm.getObjectById(UserProfileInfo.class,user.getUserId());
    int presize = userProfile.getAccounts().size();
    AccountInfo ai = userProfile.removeAccount(id);
    int postsize = userProfile.getAccounts().size();
    UserProfileInfo committed = (UserProfileInfo)pm.makePersistent(userProfile);
    int postcommitsize = committed.getAccounts().size();
    pm.close();

下面是userprofileinfo类的相关部分:

@PersistenceCapable(identityType = IdentityType.APPLICATION)
class UserProfileInfo {
  @Persistent
  private Set<AccountInfo> accounts;

public AccountInfo removeAccount(Long id) throws Exception {
    Iterator<AccountInfo> it = accounts.iterator();
    StringBuilder sb = new StringBuilder();
    while(it.hasNext()) {
        AccountInfo acctInfo = it.next();
        Long acctInfoId = acctInfo.getId();
        if(acctInfoId.equals(id)) {
            it.remove();
            return acctInfo;
        }
        sb.append(" ");
        sb.append(acctInfoId);
    }
    throw new Exception("Cannot find id " + id + " Tried " + sb.toString());
  }
}