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Yaroslav Shmarov
Yaroslav Shmarov

Posted on • Originally published at blog.corsego.com on

Polymorphysm 101. Part 1 of 3. Polymorphyc Comments.

#ruby #rails #polymorphism

My current best approach for creating polymorphic child records based on the best bits from all other approaches.

This example - creating polymorphic Comments table that can be integrated easily into any model.

polymorphic-comments.gif

Step 1. Add polymorphic comments to the application

console

rails g migration create_comments content:text commentable:references{polymorphic}
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app/models/comment.rb

class Comment < ApplicationRecord belongs_to :commentable, polymorphic: true validates :content, presence: true def to_s content end end
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app/controllers/comments_controller.rb

class CommentsController < ApplicationController before_action :set_commentable def new @comment = Comment.new end def create @comment = @commentable.comments.build(comment_params) if @comment.save redirect_to @commentable, notice: "Comment created" else render :new end end def destroy @comment = Comment.find(params[:id]) if @comment.destroy redirect_to @commentable, notice: "Comment deleted" else redirect_to @commentable, alert: "Something went wrong" end end private def comment_params params.require(:comment).permit(:content) end def set_commentable if params[:user_id].present? @commentable = User.find_by_id(params[:user_id]) elsif params[:lesson_id].present? @commentable = Lesson.find_by_id(params[:lesson_id]) end end end
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app/views/comments/_form.html.erb

<%= form_for [@commentable, @comment] do |f| %> <% if @comment.errors.any? %> <% @comment.errors.each do |error| %> <%= error.full_message %> <% end %> <% end %> <%= f.label :content %> <%= f.text_area :content %> <%= f.submit %> <% end %>
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app/views/comments/_index.html.erb

Comments: <%= @commentable.comments.count %> <% commentable.comments.each do |comment| %> <%= comment.created_at.strftime('%d-%m-%Y %H:%m') %> <%= link_to "Destroy", [@commentable, comment], method: :delete %> <%= simple_format(comment.content) %> <br> <% end %>
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app/views/comments/new.html.erb

New Comment for: <%= link_to @commentable, @commentable %> <%= render 'comments/form' %>
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routes.rb

 resources :lessons do resources :comments, only: [:new, :create, :destroy] end
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Step 2. Add polymorphic comments to a model. For example lesson

app/controllers/lessons_controller.rb

 def show @commentable = @lesson @comment = Comment.new end
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app/models/lesson.rb

 has_many :comments, as: :commentable, dependent: :destroy
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app/views/lessons/show.html.erb - with a link to create a comment

<%= link_to "New Comment", new_lesson_comment_path(@commentable, @comment) %> <%= render partial: "comments/index", locals: {commentable: @commentable} %>
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app/views/lessons/show.html.erb - alternative - with a comments form in the view

<%= render template: "comments/new" %> <%= render partial: "comments/index", locals: {commentable: @commentable} %>
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Notes

In comments_controller you have to update the action set_commentable with each model that you want to make commentable. This is better than creating a separate comments_controller for each commentable model.

To add polymorphic to one more model, repeat step 2 by replacing the word lesson with whatever model you want.

Bonus: Save which user created a comment

1.

rails g migration add_user_references_to_comments user:references
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  1. To save current_user who created a comment, in comments_controller create action above line if @comment.save add the line 
@comment.user_id = current_user.id
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Using simple_form 

<%= simple_form_for [@commentable, @comment] do |f| %> <%= f.error_notification %> <%= f.error_notification message: f.object.errors[:base].to_sentence if f.object.errors[:base].present? %> <%= f.input :content, label: false, required: true %> <%= f.button :submit %> <% end %>
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