iphone - 核心数据:对多关系的谓词

Question

我有一个包含 4 个实体的 CoreData 模型。

模型截图 -> http://img96.imageshack.us/img96/7857/screenshot20100209at182.png

状态

-StateName

位置:

-locationName (attribute)

-locationDescription

-locationActivities (relatinship)

-state (relationship)

位置事件:

-location (relationship)

-activity (relationship)

事件

-activityName(attribute)

-locationsActivities (relationship)

我如何编写一个查询来选择所有具有

的位置

(activity = 'Golf' OR activity = 'Swimming') AND state = 'LA'

Answer 1

// With some NSManagedObjectContext *moc
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:[NSEntityDescription entityForName:@"Location"
                               inManagedObjectContext:moc]];
[request setPredicate:[NSPredicate predicateWithFormat:
                       @"(locationActivities.activity.activityName == %@ OR 
                          locationActivities.activity.activityName == %@) AND 
                         state.stateName == %@",
                       @"Golf", @"Swimming", @"LA"]];
NSError *error;
NSArray *results = [moc executeFetchRequest:request error:&error];

基本上，像往常一样获取核心数据，然后构建适当的谓词来过滤结果(如 Predicate Programming Guide 中所述)。