NSPredicate - Unable to parse the format string [duplicate]

问题:

This question already has an answer here:

• Creating NSPredicate dynamically by setting the key programmatically 2 answers

I am trying to write a NSPredicate to fetch rows with my_column value with this string "193e00a75148b4006a451452c618ccec" and I get the below crash.

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unable to parse the format string "my_column=193e00a75148b4006a451452c618ccec"'

My predicate statement

fetchRequest.predicate=[NSPredicate predicateWithFormat:[NSString stringWithFormat:@"%@==\"%@\"",attributeName,itemValue]]; 

also tried this

fetchRequest.predicate=[NSPredicate predicateWithFormat:[NSString stringWithFormat:@"%@ == %@",attributeName,itemValue]]; 

this

fetchRequest.predicate=[NSPredicate predicateWithFormat:[NSString stringWithFormat:@"%@ = %@",attributeName,itemValue]]; 

and this

fetchRequest.predicate=[NSPredicate predicateWithFormat:[NSString stringWithFormat:@"%@=\"%@\"",attributeName,itemValue]]; 

Please help.

I found out this, when I was trying with Martin R's answer

fetchRequest.predicate=[NSPredicate predicateWithFormat:@"%@==%@",attributeName,itemValue]; 

attributeName I pass comes with a ' ' so I took off attributeName and hardcoded it, then it works fine.

回答1:

Enclose the string in single quotes:

[NSPredicate predicateWithFormat:@"my_column = '193e00a75148b4006a451452c618ccec'"] 

or better, use argument substitution:

[NSPredicate predicateWithFormat:@"my_column = %@", @"193e00a75148b4006a451452c618ccec"] 

The second method avoids problems if the search string contains special characters such as ' or ".

Remark: Never use stringWithFormat when building predicates. stringWithFormat and predicateWithFormat handle the %K and %@ format differently, so combining these two methods is very error-prone (and unnecessary).

回答2:

I think you have missed '' when checking for equality,

now try,

[NSPredicate predicateWithFormat:@"my_column='193e00a75148b4006a451452c618ccec'"]; 

回答3:

Try

//Case Insensitive fetchRequest.predicate=[NSPredicate predicateWithFormat:@"%K = [cd] %@",attributeName,itemValue];  //Case sensitive fetchRequest.predicate=[NSPredicate predicateWithFormat:@"%K = %@",attributeName,itemValue]; 

文章来源: NSPredicate - Unable to parse the format string [duplicate]