Rails polymorphic association and has_many for the same model

Question

I have the Comment model which belongs to some other models like Post, Page etc and has_one (or belongs_to?) User model. But I need the User to be commentable too, so User has to have many Comments from other Users (this is polymorphic :commentable association) and he has to have his own Comments, written by him. What is the best way to make an association like this? How can I read and create Comments for User in a controller if User has two different associations with Comments? Now I do this and it's not right I guess:

class User < ActiveRecord::Base
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable
  has_many :comments, as: :commentable
  has_many :comments
end

class Comment < ActiveRecord::Base
    belongs_to :commentable, polymorphic: true
    belongs_to :user
end

class CreateComments < ActiveRecord::Migration
  def change
    create_table :comments do |t|
      t.text :content
      t.references :commentable, polymorphic: true, index: true
      t.belongs_to :user
      t.timestamps null: false
    end
  end
end

Ven · Accepted Answer · 2016-08-30 09:32:16Z

3

You'll want to use another name for that association.

has_many :comments, as: :commentable
has_many :commented_on, class_name: 'Comment' # you might also need foreign_key: 'from_user_id'.

See has_many's documentation online.

The foreign_key should not be needed in your case, but I'm pointing it out Just In Case™. Rails will guess "{class_lowercase}_id" by default (so user_id in a class named User).

Then you can access both associations (The class_name is explicitly needed because Rails can't find Comment from commented_on).

answered Aug 30, 2016 at 9:32

Ven

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