Core data 使用属性搜索实体时的核心数据子实体ByName
我试图根据名为“name”的属性从核心数据中获取一个实体。这是我的密码:Core data 使用属性搜索实体时的核心数据子实体ByName,core-data,ios5,Core Data,Ios5,我试图根据名为“name”的属性从核心数据中获取一个实体。这是我的密码: NSManagedObjectContext *context = [self managedObjectContext]; NSEntityDescription *vegetable = [NSEntityDescription insertNewObjectForEntityForName:@"Vegetable" inManagedObjectContext:context]; // get
NSManagedObjectContext *context = [self managedObjectContext];
NSEntityDescription *vegetable = [NSEntityDescription insertNewObjectForEntityForName:@"Vegetable" inManagedObjectContext:context];
// get the vegetable using name
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSPredicate *predicate =
[NSPredicate predicateWithFormat:@"name == %@", myGardenViewModel.vegetable.name];
[request setEntity:vegetable];
[request setPredicate:predicate];
NSError *error;
NSArray *fetchedObjects = [self.managedObjectContext executeFetchRequest:request error:&error];
最后一行引发以下异常:
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Vegetable subentitiesByName]: unrecognized selector sent to instance 0x6bbcdd0'
有什么想法吗?问题在于如何设置
NSFetchRequest
的实体
属性。使用insertNewObjectForEntity:
您实际上是在创建一个新对象,以便稍后使用[managedObjectContext save:&error]插入到数据库中代码>
您要做的是只为获取请求设置实体,而不是插入新对象:
NSEntityDescription *vegetable = [NSEntityDescription entityForName:@"Location"
inManagedObjectContext:self.managedObjectContext];