核心数据驱动应用程序的一个常见场景是从后备存储中获取唯一对象。如果具有某个唯一属性的对象存在,则返回该对象,如果它不返回新创建的对象。我发现自己一遍又一遍地写同样的东西,所以我用一种方便的方法把它包装起来。但这似乎微不足道,我在这里重新发明轮子吗?有没有更简单、开箱即用的方法来实现这一目标?
干杯,
EP
+(id)uniqueEntityfForName:(NSString *)name
withValue:(id)value
forKey:(NSString *)key
inManagedObjectContext:(NSManagedObjectContext *)context {
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
request.entity = [NSEntityDescription entityForName:name inManagedObjectContext:context];
request.predicate = [NSPredicate predicateWithFormat:[key stringByAppendingString:@" == %@"], value];
NSArray *result = [context executeFetchRequest:request error:nil];
id entity = [result lastObject];
if (entity == nil) {
entity = [NSEntityDescription insertNewObjectForEntityForName:name inManagedObjectContext:context];
[entity setValue:value forKey:key];
} else {
entity = [result lastObject];
}
return entity;
}
我使用这种方法是这样的:
SomeEntity *entity = [CDUtils uniqueEntityfForName:@"SomeEntity" withValue:@"foo" forKey:@"bar" inManagedObjectContext:context];