Question

我有2个这样的表：

 Users
 user_id (pk)
 email
 name
 inGroups (many to many relationship with groups)

 Groups
 group_id (pk)
 group_name
 whoseUsers (many to many relationship with users)

我的核心数据代码如下：

NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Users"];
request.predicate = [NSPredicate predicateWithFormat:@"user_id = %@ AND inGroups = %@", user_id, group_id];

运行此操作时，我会抛出异常：

@"to-many key not allowed here"

如何使其正常工作？

Answer 1

要查找给定user_id的用户，这些用户是具有给定group_id的群组的成员，使用

[NSPredicate predicateWithFormat:@"user_id = %@ AND ANY inGroups.group_id = %@",
                                   user_id, group_id];

Answer 2

首先不要使用= use ==喜欢这个“user_id ==％@ AND inGroups ==％@”其次如果是多对多的关系那么它就是一个NSSet。你在这里尝试做的是将NSSet关系与group中的group_id进行比较。编辑你应该做这样的事情 NSFetchRequest * request = [NSFetchRequest fetchRequestWithEntityName：@“Users”];

request.predicate = [NSPredicate predicateWithFormat：@“user_id ==％@ AND inGroups CONTAINS％@”，user_id，group];

其中group是actuall Groups对象

使用NSPredicate验证多对多关系

2 个答案: