# ActiveRecord::Migration is a mix-in?

**URL:** <https://www.ruby-forum.com/t/activerecord-migration-is-a-mix-in/120956>\
**Category:** Rails\
**Created:** [November 22, 2007, 4:14am UTC](https://www.ruby-forum.com/t/activerecord-migration-is-a-mix-in/120956 "2007-11-22T04:14:56Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![Thufir](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ee7513/32.png) [@Thufir](https://www.ruby-forum.com/u/Thufir)\
**Post date:** [November 22, 2007, 4:14am UTC](https://www.ruby-forum.com/t/activerecord-migration-is-a-mix-in/120956/1 "2007-11-22T04:14:56Z")

</div>

I’m going by [http://railsforum.com/viewtopic.php?id=1011](http://railsforum.com/viewtopic.php?id=1011) and am  
curious  
about this line:

class AddUserIdToPosts \< ActiveRecord::Migration

AddUserIdToPosts is a class, ok. ActiveRecord is a module, ok.  
Migration is a class? This is an example of a mix-in?

I don’t really understand this line ☹

-Thufir