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

An old question, but there is a cleaner way of achieving this by setting up a direct association for the specific type along with the polymorphic:

#comment.rb
class Comment < ActiveRecord::Base

  belongs_to :commentable, polymorphic: true
  belongs_to :forum_topics, -> { where( comments: { commentable_type: 'ForumTopic' } ).includes( :comments ) }, foreign_key: 'commentable_id'

  ...

end

You are then able to pass :forum_topics to includes getting rid of the need for a messy join:

@comments = Comment
  .includes( :forum_topics )
  .where( :forum_topics => { featured: true } )

You could then further clean this up by moving the query into a scope:

#comment.rb
class Comment < ActiveRecord::Base

  ...

  scope :featured_topics, -> { 
    includes( :forum_topics )
    .where( :forum_topics => { featured: true } ) 
  }

  ...

end

Leaving you to be able to simply do

@comments = Comment.featured_topics