The ability to like or favorite posts is very common on websites. This guide will show you how to add this functionality to your Rails 5 application without adding unnecessary bloat from gems. This guide assumes that you have already implemented posts (or similar) and users to your application and will not cover these steps.

Let's go over some design considerations before we begin. While everyone can view a post, only authenticated users can like posts by clicking a link or icon.  We're keeping it positive by just tracking likes.

Creating the Likes model

We're going to start by creating a model that represents the association between users and the posts they like. This will be a join table called 'Like'.  If you need, you can use a different name and update the views and controllers to match.

rails g model Like user_id:integer post_id:integer

If the user has a record for a post in the Likes table, then the user likes the post.  If no record exists, the user either does not like the post or has not voted yet.



Don't forget to run

rake db:migrate

Create the routes for likes

We're going to define the rout using nested resources like so:

  resources :posts do

    resource :like

  end

As you can see, we have added a singular resource. This will allow the user to only have one like on each post. This construction also works best with how we are designing our controller as you will see.



Typically, we would create a LikesController in the controller folder, but we're actually going to scope the controllers and routes under posts.

  resources :posts do

    resource :like, module: :posts

  end

Now if you check your routes, you'll see that likes are scoped under a posts folder.

Adding the files and folders

We can easily created the needed folders in the terminal with: 

mkdir app/controllers/posts

and

mkdir app/views/posts/likes

Now we can create the LikesController at app/controllers/posts/likes_controller.rb

class Posts::LikesController < ApplicationController

 before_action :authenticate_user!


  def create

    @post.likes.where(user_id: current_user.id).first_or_create

    respond_to do |format|

      format.html { redirect_to @post }

      format.js

    end

  end

  private

    def set_post

      @post = Post.find(params[:post_id])

    end

end

Let's go over this code. In the create action we're looking up the likesfor the post based on the current_user's id. Then we use the first_or_create method to get the first record or create a new one. This will prevent us from duplicates.



Next we created a respond_to block and send the HTML requests to be redirected to the posts and creates a JS response to render the template instead of redirecting back.



Now it's time to create the file that makes our solution work, app/views/posts/_likes.html.erb:

<% if user_signed_in? && current_user.likes?(@post) %>

<%= link_to "Unlike", post_like_path(@post), method: :delete %>

<% else %>

<%= link_to "Like", post_like_path(@post), method: :post %>

<% end %>

In this snippet, we check that the user is signed in and that the user likes the post. If this is the case, we display an 'unlike' link which deletes the record. If the user isn't signed in or has not liked the post, a 'like' link is displayed.

Implementing the solution

Let's start a reference the partial that we created earlier by adding the following to app/views/posts/show.html.erb:

<div id="likes">

  <%= render partial: "likes" %>

</div>


Next we're going to update our User model to use the likes?() method as follows:

# User.rb

has_many :likes


def likes?(post)

  post.likes.where(user_id: id).any?

end

At this point, you should be able to like a post and then see the 'unlike' link. However, you should receive an error because we haven't created a 'destroy' action in our LikesController. Let's implement that:

  def destroy

    @post.likes.where(user_id: current_user.id).destroy_all


    respond_to do |format|

      format.html { redirect_to @post }

      format.js

    end

  end

This is very similar to the create action but uses destroy_all instead of first-or_create. 

Rendering a Javascript response

With this implemented, we've created the ability to like and unlike, but we're not rendering a Javascript response. This is actually pretty simple as we've already laid most of the groundwork. We already created a div with an id of 'likes' in app/views/posts/show.html.erb to help with this. First, lets add remote:true options to the likes partial:

<% if user_signed_in? && current_user.likes?(@post) %>

<%= link_to "Unlike", post_like_path(@post), method: :delete, remote: true %>

<% else %>

<%= link_to "Like", post_like_path(@post), method: :post, remote: true %>

<% end %>

Now the app expects a Javascript response and will render that response on the page instead of reloading. Let's create the responses that will be needed.

app/views/posts/likes/create.js.erb

$("#likes").html("<%= j render partial: 'posts/likes' %>");

app/views/posts/likes/destroy.js.erb

$("#likes").html("<%= j render partial: 'posts/likes' %>");

Refining the code

We could add liking functionality to the post index by adding:



app/views/posts/index.html.erb

<p><%= render partial: 'likes' %></p>

This will give us an error because the @post variable is not set. We need to edit our partial and the code referencing the partials to work with the locals option.



app/views/posts/index.html.erb

 

<%= render partial: 'likes', locals: { post: post } %>

Let's also update the references in app/views/posts/show.html.erb 

 

<div id="likes">

  <%= render partial: 'likes', locals: { post: @post } %>

</div>

 app/views/posts/likes/create.js.erb and app/views/posts/likes/destroy.js.erb  

$("#likes").html("<%= j render partial: 'posts/likes', locals: {post: @post } %>");

app/views/posts/_likes.html.erb

<% if user_signed_in? && current_user.likes?(post) %>

<%= link_to "Unlike", post_like_path(post), method: :delete, remote: true %>

<% else %>

<%= link_to "Like", post_like_path(post), method: :post, remote: true %>

<% end %>


<%= post.likes.count %>

<% post.likes.each do |like| %>

  <%= image_tag like.user.avatar_url, width: 20 %>

<% end %>

Now we should be able to view likes on the posts index, but if you click like it won't display correctly. We need to go into our responses and change them to work with the divs to get the post id.



app/views/posts/likes/create.js.erb and app/views/posts/likes/destroy.js.erb

$("#post_<%= @post.id %>_likes").html("<%= j render partial: 'posts/likes', locals: {post: @post } %>");

We need to go back to add the id to our index and show views.

 

app/views/posts/index.html.erb

<p id="post_<%= post.id %>_likes"><%= render partial: 'likes' %></p>

post/show.html.erb

<div id="post_<%= @post.id %>_likes">

  <%= render partial: 'likes', locals: { post: @post } %>

</div>

Now the _likes partial is more flexible and tied to the appropriate posts.

Taking it further

Things you can do to extend this app:

• Display number of likes


• Display avatars of users who have liked


• Track dislikes