我正在尝试设置核心数据，但是当我在UIManagedDocument上运行saveToURL时，它无法创建它。这是我的代码；@property(nonatomic,strong)UIManagedDocument*currentUserDatabase;@synthesizecurrentUserDatabase=_currentUserDatabase;-(void)setCurrentUserDatabase:(UIManagedDocument*)currentUserDatabase{_currentUserDatabase=currentUserDatabase;[selfu