批处理对象集合的多对多关系

Question

场景:

比方说,我有一个名为实体,Author即有一个叫做一对多关系books的Book实体(反向关系author).如果我有一个现有的Author对象集合,我想books在一个获取请求中为所有这些对象的关系出错.

码

这是我到目前为止所尝试的:

NSArray *authors = ... // array of `Author` objects
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Book"];
fetchRequest.returnsObjectsAsFaults = NO;
fetchRequest.predicate = [NSPredicate predicateWithFormat:@"author IN %@", authors];

执行此获取请求不会导致数组中books对象的关系authors出现故障(通过日志记录进行检查).

我也试过反过来做提取请求:

NSArray *authors = ... // array of `Author` objects
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Author"];
fetchRequest.returnsObjectsAsFaults = NO;
fetchRequest.predicate = [NSPredicate predicateWithFormat:@"SELF IN %@", authors];
fetchRequest.relationshipKeypathsForPrefetching = @[@"books"];

这也不会引发故障.这样做的恰当方式是什么？