Value Expressions: Where to Find Documentation

When you open a mapping model in a Core Data project, you’ll see that attributes and relationships have a value expression, and you have the option to change the value expression. For attributes the value expression is usually simple.

$source.AttributeName

I wanted to see what kinds of values you could give a value expression. I did a Google search and found some questions from people on mailing lists and message boards from people who wanted the same information as I did. But I found no answers. After doing some more searching, I learned an important piece of information.

A value expression is an object of the NSExpression class. With this information I could look at Apple’s documentation. The place to start is the NSExpression class reference. In the class reference is a link to Apple’s Predicate Programming Guide. After looking at both documents, I learned value expressions are a large topic with many possible values, too many for me to answer here. But I now know where to look when I need information on value expressions. Now you know where to look too.