Favorite candy

candy.rb

#== Migrations

class CreateUsers < ActiveRecord::Migration[5.0]
  def change
    create_table :users do |t|
      t.string :name
      t.timestamps
    end
  end
end

class CreateCandies < ActiveRecord::Migration[5.0]
  def change
    create_table :candies do |t|
      t.string :name
      t.timestamps
    end
  end
end

class CreateFavorites < ActiveRecord::Migration[5.0]
  def change
    create_table :favorites do |t|
      t.references :favoritable, polymorphic: true
      t.references :user
      t.timestamps
    end
  end
end

#== Models

class User < ActiveRecord::Base
  has_many :favorites
end

class Candy < ActiveRecord::Base
  has_many :favorites, as: :favoritable
  
  def favorite_by_user?(user)
    favorites.where(user_id: user).exists?
  end
end

class Favorite < ActiveRecord::Base
  belongs_to :favoritable, polymorphic: true
  belongs_to :user
end

#== Controller

class CandiesController < ApplicationController
  def index
    @candy = Candy.all
  end
end

index.erb

<% @candy.each do |candy| -%>
  <%= candy.name %>
  <% if candy.favorite_by_user?(current_user) -%>
    ♥
  <% end -%>
<% end %>