Sams Teach Yourself Core Data for Mac® and iOS in 24 Hours

Hour 10. Working with Predicates and Sorting

What You’ll Learn in This Hour:

• Selecting data the Core Data way

• Constructing predicates

• Sorting data two ways

Understanding Predicates

A predicate is a logical operator that evaluates to a Boolean value—true or false. Many people think of a predicate as the WHERE clause in a SQL statement, but that is only one particular case. In SQL, you can write the following:

SELECT name, address FROM employee WHERE department = 'research';

department = 'research' serves as the predicate. For each record that might be returned by the SELECT statement, department = 'research' is evaluated based on that record’s data and the result is either true or false. The records where the result is TRUE are returned ...