iOS: NSPredicate doesn't work correct

问题

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?

回答1:

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.

来源：https://stackoverflow.com/questions/22514335/ios-nspredicate-doesnt-work-correct