核心数据 - 获取不在关系中的所有对象 [英] Core Data - Fetch all objects NOT in a relationship

问题描述

我有一个与实体B具有一对多关系的核心数据实体A.给定一组实体B的实例，如何检索不与这些实例的关系中的A的所有实例B？ （我在说iOS核心数据，如果这很重要）。

I have a core data entity A that has a one-to-many relationship with entity B. Given a set of instances of entity B, how do I retrieve all instances of A that are NOT in a relationship with those instances of B? (I'm talking about IOS core data, if that matters).

推荐答案

NSSet *bEntities = a.b;
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF NOT IN %@", bEntities];
NSManagedObjectContext *moc = ...;
NSFetchRequest *fetchRequest = [[[NSFetchRequest alloc] init] autorelease];
[fetchRequest setEntity:[NSEntityDescription entityForName:@"B" inManagedObjectContext:moc]];
NSArray *result = [moc executeFetchRequest:fetchRequest];

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