如何获取Core Data中的关系项属性？ [英] How to get at a relationship items properties in Core Data?

问题描述

假设你有一个名为Workshop的核心数据对象。

如何在Workshop中创建学生的NSArray？

这是一个与数组相反的NSSet，因为它们是无序的。使用mutableSetValueForKey：这个
返回一个代理，它会改变
关系并执行KVO
通知。想想名字为
[NS] MutableSetvalueForKey而不是b的b比mutableSetValueforKey，
因为它返回一个可变集合
你操作

  NSMutableSet *学生; 
 Students = [Workshop mutableSetValueForKey：@Students]; 
 [Students addObject：newStudent]; 
 [Students removeObject：oldStudent]; 
  

来源

Say you have a Core Data object called Workshop. It has a to-many relationship to a Student object.

How would I create an NSArray of the students within the Workshop?

解决方案

It's a NSSet opposed to an array, as they are unordered.

Use mutableSetValueForKey: This returns a proxy that mutates the relationship and does KVO notifications. Think of the name as "[NS]MutableSet" "valueForKey" rather than "mutableSetValue" "forKey", because it returns a mutable set that you manipulate

NSMutableSet *Students;
Students = [Workshop mutableSetValueForKey: @"Students"];
[Students addObject: newStudent];
[Students removeObject: oldStudent];

source

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