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  • Achieving Nested Comments in Rails

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    Few days back, I was working on a project where I have to create nested comments on a articles and on showing the article I was needed to show all the nested comments in its hierarchy.So I used closure_tree gem to achieve that. So lets see how I implemented the nested comment functionality on article.

    1) Add the following Gem to your Gemfile.

    gem 'closure_tree'

    2) Run the bundle to install the Gem


    3) Now create the comments model which will have article_id (in case of root comment which will be posted directly on the article), parent_id (for storing the parent comment id), user_id, text (to store the content of the text)

    rails g model Comment article:references parent_id:integer text:string

    4) Now run the following migration for getting nested comments hierarchy

    rails g migration create_comment_hierarchies

    5) Inside this migration write the following code

    class CreateCommentHierarchies < ActiveRecord::Migration
      def change
        create_table :comment_hierarchies, :id => false do |t|
          t.integer  :ancestor_id, :null => false   # ID of the parent/grandparent/great-grandparent/... comments
          t.integer  :descendant_id, :null => false # ID of the target comment
          t.integer  :generations, :null => false   # Number of generations between the ancestor and the descendant. Parent/child = 1, for example.
        # For "all progeny of" and leaf selects:
        add_index :comment_hierarchies, [:ancestor_id, :descendant_id, :generations],
                  :unique => true, :name => "comment_anc_desc_udx"
        # For "all ancestors of" selects,
        add_index :comment_hierarchies, [:descendant_id],
                  :name => "comment_desc_idx"

    6) Inside Comment model write this line

    acts_as_tree order: 'created_at DESC'
    belongs_to :parent, class_name: "Comment"
    has_many :childrens, class_name: "Comment", foreign_key: "parent_id"

    7) Now during creation of the comment you need to create the comment like this:

    def create
      if params[:comment][:parent_id].present?
        parent = Comment.where(params[:comment][:parent_id]).first
        comment =
        comment =
       	render json: {success: true, message: "Comment Created Successfully"}
         render json: {success: false, message: "Something went wrong"}

    8) Now to get the hierarchy of a comment you just need to write like this:


     and it will give you a result set like this:

     {"k1l1" =>
    	{"k1l2" =>
    	   {"k1l3" =>
    	     {"k1l4" => {}
    	   "k2l3" =>
    	     {"k2l4" => {}}
    	   "k3l3" => {}

    You can also define the depth limit of the tree:

    Comment.hash_tree(limit_depth: 2)


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