iOS：NSPredicate不工作正确 [英] iOS: NSPredicate doesn't work correct

问题描述

我尝试用谓词表达搜索参数：

  NSPredicate * predicate = [NSPredicate predicateWithFormat：@name CONTAINS [ cd]％@ OR code CONTAINS [cd]％@ OR currency CONTAINS [cd]％@ AND continent.paid ==％@，searchString，searchString，searchString，[NSNumber numberWithBool：YES]]; 
  

我尝试为可能的字符串记录表达搜索参数只有continent.paid == YES。问题是最后一个表达式被忽略。搜索返回来自continent.paid == NO的数据以及正确的数据。

b p $ p> [NSPredicate predicateWithFormat：@（name CONTAINS [cd]％@ OR code CONTAINS [cd]％@ OR currency CONTAINS [cd]％@）AND continent.paid ==％@ ，
searchString，searchString，searchString，[NSNumber numberWithBool：YES]];


据我所知，AND和OR在谓词中具有相同的优先级，并从左到右评估
。因此，在你的代码中，如果CONTAINS表达式的一个
为真，则谓词计算为 true 。

I try to express the search parameters with predicate:

NSPredicate *predicate=[NSPredicate predicateWithFormat:@"name CONTAINS [cd] %@  OR code CONTAINS [cd] %@ OR currency CONTAINS [cd] %@ AND continent.paid == %@",searchString,searchString,searchString,[NSNumber numberWithBool:YES]];

I try to express search parameters for possible string records ONLY where continent.paid==YES. The problem is that last expression is ignored. The search returns data from continent.paid==NO as well with the correct data. Whats wrong with it?

解决方案

You have to set parentheses:

[NSPredicate predicateWithFormat:@"(name CONTAINS [cd] %@  OR code CONTAINS [cd] %@ OR currency CONTAINS [cd] %@) AND continent.paid == %@",
         searchString,searchString,searchString,[NSNumber numberWithBool:YES]];

As far as I know, "AND" and "OR" have the same precedence in a predicate, and are evaluated from left to right. Therefore in your code, the predicate evaluates to true if one of the "CONTAINS" expressions is true.

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