NSPredicate在NSSet中找到具有属性的对象

问题描述

我有一个 NSMangedObject ，其中包含 NSSet 其他 NSManagedObjects

我需要检查这些对象是否在 NSSet 中有一个值，然后返回它们。 p>

我使用MagicalRecord来获取数据。

所以我需要这样的：

  NSPredicate * predicate = [NSPredicate predicateWithFormat：@stringObjects contains％@，string]; 
 

所以如果NSSet stringObjects包含一些我正在寻找的字符串，那么返回对象我已经请求。 / p>



注意这里：stringObjects（名称只是为了代表我的 NSSet ）它是 NSSet 包含NSManagedObjects，所以我需要通过一些id（例如string_id属性）来搜索它们。

/ p>

  NSSet * set = MainObject.stringObjects; 
 NSString * string_id_for_first_object = [[[set allObjects] objectAtIndex：0] string_id]; 
  

只是为了更好地理解关系。

但是问题是如何创建谓词来检查NSSet是否包含所需的id。

解决方案

如果我正确理解你的问题， stringObjects 是从一个实体 A 到另一个实体 B 的一对多关系
， > B 具有 string_id 的属性。

与给定 string id 的任何 B 对象相关的对象，请使用：

  NSString * stringId = ...; //你正在寻找的字符串
 NSPredicate * predicate = [NSPredicate predicateWithFormat：@ANY stringObjects.string_id ==％@，stringId]; 
  

I have an NSMangedObject that contains NSSet of other NSManagedObjects.

I need to check if these objects has an value in NSSet and then return them.

I use MagicalRecord for fetching data.

So I need something like this:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"stringObjects contains %@", string];

So if NSSet stringObjects contains some string that I am looking for so then return object I have requested.

One note here: stringObjects (name just for example it represent my NSSet) it is NSSet that contains NSManagedObjects, so I need to search them by some id (for example string_id attribute).

So then model looks like this

NSSet *set = MainObject.stringObjects;
NSString *string_id_for_first_object = [[[set allObjects] objectAtIndex:0] string_id];

Just for better understanding relationship.

But the question is about how can I create predicate to check if NSSet contains needed id.

解决方案

If I understand your question correctly, stringObjects is a to-many relationshipfrom one entity A to another entity B, and B has an attribute string_id.

To find all A objects that are related to any B object with the given string id, use:

NSString *stringId = …; // The string that you are looking for
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY stringObjects.string_id == %@", stringId];

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