UPDATE: If you're working with the DRUPAL-6--2 branch please see the updated code example below.

In this article I will show you how you can write a tiny bit of code that will reveal new fields and facets for searching with the ApacheSolr module and Acquia Search. Using Acquia Drupal we'll write an example module that takes the file type from CCK file and image fields and makes them into their own search fields. This results in us being able to filter our search results based on file type. This code fulfils the situation where you want, for example, to find a specific post that has a JPEG image, or all of the posts with PDFs that match a particular keyword.