NSPredicate：CoreData fetchRequest按字典数组过滤 [英] NSPredicate : CoreData fetchRequest filtered by Array of dictionaries

问题描述

是否可以使用字典数组创建NSPredicate？

我有以下结构：

  [{name：foo，city：Paris}，{name：bar，city：London}] 
  

我想通过这些对过滤我的 NSFetchRequest （假设属性在CoreData中具有相同的名称）

当传递数组时，我可以使用关键字 IN 。但我不知道如何使这个工作与一个字典数组。

解决方案

我不认为你将能够使用 IN ，因此您需要使用一些 OR 。大纲：

1. 迭代数组的所有元素。



2. （ dictionary ），构造一个形式的谓词：

     predicateWithFormat：@name ==％@ AND city ==％@，[dictionary objectForKey：@name]，[dictionary objectForKey：@city]]; 
     




3. 将每个此类谓词添加到NSMutableArray（数组

   p> [NSCompoundPredicate orPredicateWithSubpredicates：array]





如果性能是一个问题，请考虑使用替换变量而不是格式来构建单个谓词。

Is it possible to create an NSPredicate using an array of dictionaries ?

I have a following structure :

[{ name: "foo", city:"Paris"},{name:"bar", city:"London"}]

An I want to filter my NSFetchRequest by these pairs. (supposing the properties have the same names in CoreData)

When passing an array I can use the keyword IN. But I don't get how make this work with an array of dictionaries.

解决方案

I don't think you will be able to use IN, so you need to use a number of ORs. In outline:

1. Iterate through all elements of the array.

2. For each element (dictionary), construct a predicate of the form:

   [NSPredicate predicateWithFormat:@"name == %@ AND city == %@",[dictionary objectForKey:@"name"], [dictionary objectForKey:@"city"]];
   

3. Add each such predicate to a NSMutableArray (array) of predicates

4. Build a compound predicate from the array using:

   [NSCompoundPredicate orPredicateWithSubpredicates:array]
   

If performance is an issue, consider building the individual predicates with substitution variables rather than with format.

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