C# – Could not find an implementation of the query pattern for source type – ‘Select’ not found.

Problem

You’re getting the following error when compiling:

Could not find an implementation of the query pattern for source type ‘Your Type’.  ‘Select’ not found.

Solution

The error message is odd, but the solution is simple. Add this:

using System.Linq;

I’ve only ran into this in older versions of VS.