Setting up polymorphic "likes" on posts, photos, and comments

_activity_footer.html.erb

<footer>
  <!-- here we'll toggle the links to "Like" and "Unlike" -->
  <%= display_like_unlike(object) %>
  
  <!-- if there are any likes, they'll be displayed here -->
  <%= render 'shared/likes', object: object %>
  ...
</footer>

_likes.html.erb

<!-- views/shared/_likes.html.erb -->

<% if object.has_likes? %>
  <p class='likes'>
    Likes: <%= object.likes_count %>
   <%= list_likes(object.likes) %>...
  </p>
<% end %>

concerns.rb

# Use concerns to DRY up model associations

# models/likes.rb
class Like < ApplicationRecord
# ...
  belongs_to :likeable, polymorphic: true
# ...
end


# models/comment.rb
class Comment < ApplicationRecord
#...
  belongs_to :commentable, polymorphic: true
  include Liking
#...
end


# models/photo.rb
class Photo < ApplicationRecord
# ...
  # use concerns to DRY up model associations
  include Liking
  include Commenting  
# ...
end


# models/post.rb
class Post < ApplicationRecord
# ...
  # use concerns to DRY up model associations
  include Liking
  include Commenting
# ...
end


# models/concerns/liking.rb
module Liking
  extend ActiveSupport::Concern

  included do
    has_many :likes, as: :likeable
  end

  def has_likes?
    likes.any?
  end

  def likes_count
    likes.count
  end
end



# models/concerns/commenting.rb
module Commenting
  extend ActiveSupport::Concern

  included do
    has_many :comments, as: :commentable
  end

  def has_comments?
    comments.any?
  end
end

likes_controller.rb

# controllers/likes_controller.rb
class LikesController < ApplicationController

  def create
    session[:return_to] ||= request.referer

    set_parent
    # create the like as a child in the collection of the parent class
    @like = @parent.likes.new(user_id: current_user.id)
    if @like.save
      redirect_to session.delete(:return_to)
    else
      flash[:error] = "Something went wrong."
      redirect_to session.delete(:return_to)
    end
  end

  def destroy
    session[:return_to] ||= request.referer

    set_parent
    author = @parent.user
    like = Like.find(params[:id])
    like.destroy
    redirect_to session.delete(:return_to)
  end


  private

  def like_params
    params.require(:likeable).permit(:post_id, :comment_id, :user_id)
  end

  def set_parent
    # Determine the parent class of the like by grabbing the text from the `likeable` param
    klass_name = params[:likeable]
    # Generate the name of the parent id param based on the likeable class
    parent_key = params.keys.select{|k| k.match(klass_name.downcase + '_id')}.first
    # Use the parent param name to get the value of the parent id
    id = params[parent_key]
    # Find the parent object by its id
    @parent = klass_name.constantize.find(id)
  end


end

likes_helper.rb

# helpers/likes_helper.rb

module LikesHelper

  def list_likes(likes)
    # "likes" are limited to showing only 3, and the tricky part was displaying them as links that are comma separated
    raw(likes.limit(3).map do |like|
      link_to like.user.name, user_timeline_path(like.user)
    end.join(", "))
  end

  # This method handles displaying links to create/destroy objects of multiple classes
  def display_like_unlike(object)
    klass = object.class.to_s
    like = object.likes.to_a.find { |l| l.user_id == current_user.id }
    if like == nil
      # Use polymorphic_url instead of a url helper to build the url for liking and unliking of objects of different classes.
      # The `likeable: klass` will be used by the controller to set the like's parent 
      link_to 'Like', polymorphic_url([current_user, object, :likes], likeable: klass), method: :post
    else
      link_to 'Unlike', polymorphic_url([current_user, object, like], likeable: klass), method: :delete
    end
  end

end

show.html.erb

<!-- views/timelines/show.html.erb -->
...
# an "activity" can be a text "post" or a "photo" post
<% @timeline.activities.each do |activity| %>
  
  <!-- this syntax will automatically render the correct text or photo post based on its class -->
  <%= render activity %>
<% end %>



<!-- And those partials are: -->

<!-- 1) views/photos/_photo.html.erb -->
<% unless photo.new_record? %>
  <article class="activity">

    <%= render 'shared/activity_header', object: photo %>

    <section class="activity-body">
      <%= image_tag photo.photo_data.url(:feed) %>
    </section>

    <!-- the "liking" functionality lives here in the footer -->
    <%= render 'shared/activity_footer', object: photo %>

  </article>
<% end %>


<!-- 2) views/posts/_post.html.erb -->
<% unless post.new_record? %>
  <article class="activity">

    <%= render 'shared/activity_header', object: post %>

    <section class="activity-body">
      <p><%= post.body %></p>
    </section>

    <!-- the "liking" functionality lives here in the footer -->
    <%= render 'shared/activity_footer', object: post %>

  </article>
<% end %>