CoreData predicate: string property length?

Question

Say if I have an entity Fragment, it has an attribute \'text\' which is a string, I want to query the list of Fragment whose text is o

Answer 1

You cannot use Objective-C functions like length in a Core Data fetch request. But you can replace it with the "LIKE" operator, which does a simple pattern matching:

[NSPredicate predicateWithFormat:@"text LIKE %@", @"?????"];

An interesting point is that Core Data does not throw an exception or return with an error, but just ignores the length method, i.e. it just uses the predicate "text = '5' instead. This can be seen by activating Core Data debug output by setting the launch argument

-com.apple.CoreData.SQLDebug 3

(which is generally a good method to locate Core Data fetch problems).

Answer 2

I think that it's taking text.lengh as a relationship. Try to set a predicate only with position and then do a loop looking for text.length == 5.

Answer 3

There is no length attribute for strings in the NSPredicate. Use regex instead. Your predicate should look as follows:

[NSPredicate predicateWithFormat:@"position == %@ AND text MATCHES %@", pos, @".{5}"];