ActiveRecord - querying polymorphic associations

Question

I am using polymorphic associations to track Comments in my project. All very straight forward stuff.

The problem I have is in querying based on the polymorphic asso

Answer 1

You Need a Conditional, Plus Rails 3+

A lot of people alluded to it in the answers and comments but I felt that people, including myself, would get tripped up if they landed here and didn't read thoroughly enough.

So, here's the proper answer, including the conditional that is absolutely necessary.

@comments = Comment.joins( "INNER JOIN forum_topics ON comments.commentable_id = forum_topics.id" )
                   .where( comments:     { commentable_type: 'ForumTopic' } )
                   .where( forum_topics: { featured:         true         } )

Thanks to all, especially @Jits, @Peter, and @prograils for their comments.