NSFetchRequest 不返回任何内容

任何人都可以发现为什么这不返回任何 ManagedObjects 吗？我试图将以下内容添加到 ATNSManagedObject+EasyFetching 类中，但获取结果不返回任何内容。如果我在 EasyFetch 类之外获取这些对象，我有 100 多个对象，所以我知道它不是 CoreData 为空。

+ (void)deleteAllObjectsInContext;
{
    NSManagedObjectContext *context = [NSManagedObjectContext defaultContext];
    NSEntityDescription *entity = [self entityDescriptionInContext:context];
    NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
    [request setEntity:entity];
    //[request setIncludesPropertyValues:NO];

    NSError *error = nil;
    NSArray *results = [context executeFetchRequest:request error:&error];
    if (error != nil)
    {
        //handle errors
        NSLog(@"delete error");
    }

    for (NSManagedObject *thing in results) {  <--- |results shows 0 objects|
        [context deleteObject:thing];
    }

    NSError *saveError = nil;
    [context save:&saveError];
}

尝试将其简化为：

// first get the context or pass it in as an argument (this is usually what I do for
// a deleteAll class level method like this but your call

+ (void)deleteAllObjectsInContext:(NSManagedObjectContext*)context {

    NSFetchRequest* request = [NSFetchRequest fetchRequestWithEntityName:@ "<yourEntity>"];
    // no predicate
    // no sortDescriptors

    NSError* error = nil;
    NSArray* results = [context executeFetchRequest:request error:&error];

    if (!results || error) { // nil is an error
        // handle error
    }

    // do something with results

}

这样您就可以避免检索 NSEntityDescription 对象。

UPDATE:

只是想添加这个passage https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/CoreDataFramework/Classes/NSManagedObjectContext_Class/NSManagedObjectContext.html:

返回值

“满足从接收者和与接收者的持久性存储协调器关联的持久性存储中获取的请求指定条件的对象数组。如果发生错误，则返回 nil。如果没有对象与请求指定的条件匹配，则返回空大批”。