Question

下面有两个功能，但只有一个有结果。在“noResult”中，我试图获取一个不同属性值的列表，但我得到的只是{}。

-(void)noResult {
  NSManagedObjectContext *moc= [xmppMessageArchivingStorage mainThreadManagedObjectContext];
  NSEntityDescription *entity= [NSEntityDescription entityForName:@"XMPPMessageArchiving_Message_CoreDataObject" inManagedObjectContext:moc];
  NSFetchRequest *request= [[NSFetchRequest alloc] init];
  [request setEntity:entity];
  [request setResultType:NSDictionaryResultType];
  [request setReturnsDistinctResults:YES];
  [request setPropertiesToFetch:[NSArray arrayWithObject:@"contact"]];

  NSArray *messages= [moc executeFetchRequest:request error:nil];
  NSLog(@"%@", messages); 
}

-(void)gotResult {
   NSManagedObjectContext *moc= [xmppMessageArchivingStorage mainThreadManagedObjectContext];
   NSEntityDescription *entity= [NSEntityDescription entityForName:@"XMPPMessageArchiving_Message_CoreDataObject" inManagedObjectContext:moc];
   NSFetchRequest *request= [[NSFetchRequest alloc] init];
   [request setEntity:entity];
   NSArray *messages= [moc executeFetchRequest:request error:nil];
}

以下是“gotResult” “（entity：XMPPMessageArchiving_Message_CoreDataObject; id：0x1c5d7fc0; data：{\ n bareJid = nil; \ n bareJidStr = nil; \ n body = \”Bean bags \“; \ n composing = 0; \ n contact = 1000743469142; \ n from = 7375011; \ n message = nil; \ n messageStr = nil; \ n outgoing = 0; \ n streamBareJidStr = nil; \ n thread = nil; \ n timestamp = \“2013-06-05 10:56:38 0000 \ “; \ N}）”

Answer 1

我能做出不同行为的唯一原因想到的是你在调用之前没有保存托管对象上下文使用NSDictionaryResultType获取请求。

[request setResultType:NSDictionaryResultType];

意味着

[request setIncludesPendingChanges:NO];

这意味着从fetch返回的数组反映了持久存储中的当前状态，并没有考虑上下文中的任何挂起的更改，插入或删除。

无法从Core Data获取不同的属性值

1 个答案: