grit| commit

daily learnings as a ruby dev

Rapid Prototyping with Rails: Lesson 3, part 3

26 Oct 2014

Items Covered

  1. polymorphic associations
    • databases (syntax)
    • models (syntax)
  2. Voting

Polymorphic Associations:

At the database level:

When you have one subject but many objects for example, 1 comment or like can be placed on many objects or foreign keys - postid, photoid, video_id, etc. - This creates alot of spaces and ineffiencies in the database. This is solved by restricting the database from:

"id, body, user_id, post_id, photo_id, video_id" to

 "id, body, user_id, commentable type, commentable_id"
commentable_type: must be the model name, capitialize first initial, string
 commentable_id: is the primary_key on the 1 side.

 commentable_type to commentable_id: is a composite foreign_key

In our application, we will implement voting using polymorphic associations and we can practically vote on anything, but in this case, we will vote on just posts and comments.

Step 1: Generate Migration

Create votes table
  =>rails g migration create_votes

Step 2: Generate Table

create_table :votes do |t|
  t.boolean :vote
  t.integer :user_id
  t.string :voteable_type
  t.integer :voteable_id
  t.timestamps
  end
end

or use

t.references :voteable, polymorphic: true

Step 3: Create Vote Model

class Vote < ActiveRecord::Base
  belongs_to :creator, class_name: 'User', foreign_key: 'user_id'
  belongs_to :voteable, polymorphic: true
end
class User < ActiveRecord::Base
  has_many :votes
end
class Post < ActiveRecord::Base
  has_many :votes, as: voteable
end

Do the same for comments.

The above action gives you voteable getters/setters and now you can assign a variable to your user and call .votes

So in the console:
    v = Votes.first
    v.voteable => nil
    post = Post.first
    post.votes << v
    or another way to assign is
    v.votable = Comments.first
    v.save

In the above - the user and vote are the subjects while the comments and posts are the objects being voted on.

Remember

Voting

Step 1. Now let's show votes on posts index page

#posts/index.html.erb
<div class='row'
  <div class='span0 well text-center'>
  <%= link_to '' do %>
    <i class='icon-arrow-up'></i>
    <% end %>
    <br/>
  <%= link_to '' do %>
    <i class='icon-arrow-down'></i>
    <% end %>
</div>

Step 2. How do we reflect the increase/decrease of votes every time the link is clicked:

#routes.rb
Two ways....
a) POST/votes => 'VotesController#create'
  - needs to pass in two pieces of information (1 - whether its the post/comment
  being voted on, 2. The post/comment id
  - also this would create another top level resource)
  - best for if you're voting on alot of objects

        How to implement this in your routes:
        resources :votes, only: [:create]

b) POST/posts/3/vote => 'PostsController#vote'
POST/posts/3/comments/4/vote => 'CommentsController#vote'
    How to implement this in your routes, you must use something called a member, where
    each action will be exposed to the member of that url

    resources :posts, except: [:destroy] do

      member do
        post :vote
      end

      (where post is the member and vote is the action)


      **rake routes | grep vote
      vote_post POST /posts/:id/vote(.:format)   post#vote

Step 3. Also what about if we want to see archives of our posts

# GET /posts/archives

  collection do
    get :archives
  end
  **rake routes | grep archives
  archives_posts GET /posts/archives(.:format)  posts#archives

So to compare using post vs get, post will require pass in an object. So basically you can create any route that you want using member, collections, and nested resources

Steps from UX

Step 4. Let's include these new routes in our posts/index.html.erb

#posts/index.html.erb
<div class='row'
  <div class='span0 well text-center'>
  <%= link_to vote_post_path(post) method: 'post' do %>
    <i class='icon-arrow-up'></i>
    <% end %>
    <br/>
  <%= link_to '' do %>
    <i class='icon-arrow-down'></i>
  <% end %>
</div>

You must specify method: 'post' because with out it the default will be the GET method and the link, post/id/vote will not work on a GET. * method: 'post' create data method: There is javascript that comes with rails that looks for anchor tags and the data-method="post", that will turn the link into an actual form and submit content.

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