rails

Polymorphic Routes in Rails

xuanchien

xuanchien

— 1 min read

In Rails, you can define a model as polymorphic like the following:

class Post
  has_many :comments, as: :commentable
end

class NewsItem
  has_many :comments, as: :commentable
end

class Comment
  belongs_to :commentable, polymorphic: true
end

And I believe your resources would look like this:

resources :posts
  resources :comments
end
resources :news_items
  resources :comments
end

And you can view all comments in a post through the link: /posts/1/comments (the path helper would be post_comments_path). The link to view all comments in a news_item would be very similar: news_items/1/comments (helper: news_item_comments_path).

However, Rails is intelligent enough to know that you have polymorphic association in your model and it can generate corresponding link based on the model you pass in. You can use helper polymorphic_path (or polymorphic_url) to get the correct link.

For example:

polymorphic_path(@post, Comment) # => posts/1/comments
polymorphic_path(@news_item, Comment) #=> news_items/1/comments

And in the controller of nested resources, you can check for the presence of params[:post_id] or params[:news_item_id] to know parent item you are referring to

class CommentsController < ApplicationController
  def create
    if params[:post_id]
      parent = Post.find(params[:post_id])
    else if params[:news_item_id]
      parent = NewsItem.find(params[:news_item_id])
    end

    comment = Comment.new
    comment.commentable = parent
    
    ...
  end
end

Hope this helps you refactor your code to make it look better.

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