ios 核心数据：多对多关系的 NSPredicate。（“此处不允许多对多键”）
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/4217849/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Core Data: NSPredicate for many-to-many relationship. ("to-many key not allowed here")
提问by Oh Danny Boy
I have two entities named "Category" and "Article" which have a many to many relationship. I want to form a predicate which searches for all articles where category.name is equal to some value. I have the following:
我有两个名为“类别”和“文章”的实体，它们具有多对多的关系。我想形成一个谓词，它搜索所有 category.name 等于某个值的文章。我有以下几点：
NSEntityDescription *entityArticle = [NSEntityDescription entityForName:@"Article" inManagedObjectContext:managedObjectContext];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"title" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"categories.name == [cd] %@", category.name];
[request setSortDescriptors:sortDescriptors];
[request setEntity:entityArticle];
[request setPredicate:predicate];
NSMutableArray *results = [[managedObjectContext executeFetchRequest:request error:nil] mutableCopy];
if ([results count] > 0)
NSLog(@"Results found.");
else
NSLog(@"NO results found.");
[request release];
[sortDescriptor release];
[sortDescriptors release];
The error I receive is *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'to-many key not allowed here'
我收到的错误是 *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'to-many key not allowed here'
Are there any options to retrieve the desired data?
是否有任何选项可以检索所需的数据？
回答by Dave DeLong
You're trying to compare a collection (categories.name) to a scalar value (category.name). You need to either use a collection comparator (CONTAINS), or use a predicate modifier (ANY/ALL/SOME, etc).
您正在尝试将集合 ( categories.name) 与标量值 ( category.name) 进行比较。你必须要么使用集合比较（CONTAINS），或使用谓词修饰符（ANY/ ALL/SOME等）。
Try using:
尝试使用：
[NSPredicate predicateWithFormat:@"ANY categories.name =[cd] %@", category.name];
Or:
或者：
[NSPredicate predicateWithFormat:@"categories.name CONTAINS[cd] %@", category.name];
回答by caleb81389
SWIFT SYNTAX
快速语法
In case anyone happens upon this writing in swift as I did...
万一有人像我一样迅速地看到这篇文章......
let predicate = NSPredicate(format: "ANY categories.name = %@", category.name!)
fetchRequest.predicate = predicate
worked for me.
为我工作。
