uninitialized constant User::FavoriteRecipe

So I was trying to implement a favouriting system for an app of mine and followed this guide:

The particular setup you describe mixes several types of associations.

A) User and Recipe

First we have a User model and second a Recipe model. Each recipe belonging to one user, hence we have a User :has_many recipes, Recipe belongs_to :user association. This relationship is stored in the recipe's user_id field.

$ rails g model Recipe user_id:integer ...
$ rails g model User ...

class Recipe < ActiveRecord::Base
  belongs_to :user
end

class User < ActiveRecord::Base
  has_many :recipes
end

B) FavoriteRecipe

Next we need to decide on how to implement the story that a user should be able to mark favorite recipes.

This can be done by using a join model - let's call it FavoriteRecipe - with the columns :user_id and :recipe_id. The association we're building here is a has_many :through association.

A User  
  - has_many :favorite_recipes  
  - has_many :favorites, through: :favorite_recipes, source: :recipe

A Recipe
  - has_many :favorite_recipes  
  - has_many :favorited_by, through: :favorite_recipes, source: :user 
      # returns the users that favorite a recipe

Adding this favorites has_many :through association to the models, we get our final results.

$ rails g model FavoriteRecipe recipe_id:integer user_id:integer

# Join model connecting user and favorites
class FavoriteRecipe < ActiveRecord::Base
  belongs_to :recipe
  belongs_to :user
end

---

class User < ActiveRecord::Base
  has_many :recipes

  # Favorite recipes of user
  has_many :favorite_recipes # just the 'relationships'
  has_many :favorites, through: :favorite_recipes, source: :recipe # the actual recipes a user favorites
end

class Recipe < ActiveRecord::Base
  belongs_to :user

  # Favorited by users
  has_many :favorite_recipes # just the 'relationships'
  has_many :favorited_by, through: :favorite_recipes, source: :user # the actual users favoriting a recipe
end

C) Interacting with the associations

##
# Association "A"

# Find recipes the current_user created
current_user.recipes

# Create recipe for current_user
current_user.recipes.create!(...)

# Load user that created a recipe
@recipe = Recipe.find(1)
@recipe.user

##
#  Association "B"

# Find favorites for current_user
current_user.favorites

# Find which users favorite @recipe
@recipe = Recipe.find(1)
@recipe.favorited_by # Retrieves users that have favorited this recipe

# Add an existing recipe to current_user's favorites
@recipe = Recipe.find(1)
current_user.favorites << @recipe

# Remove a recipe from current_user's favorites
@recipe = Recipe.find(1)
current_user.favorites.delete(@recipe)  # (Validate)

D) Controller Actions

There may be several approaches on how to implement Controller actions and routing. I quite like the one by Ryan Bates shown in Railscast #364 on the ActiveRecord Reputation System. The part of a solution described below is structured along the lines of the voting up and down mechanism there.

In our Routes file we add a member route on recipes called favorite. It should respond to post requests. This will add a favorite_recipe_path(@recipe) url helper for our view.

# config/routes.rb
resources :recipes do
  put :favorite, on: :member
end

In our RecipesController we can now add the corresponding favorite action. In there we need to determine what the user wants to do, favoriting or unfavoriting. For this a request parameter called e.g. type can be introduced, that we'll have to pass into our link helper later too.

class RecipesController < ...

  # Add and remove favorite recipes
  # for current_user
  def favorite
    type = params[:type]
    if type == "favorite"
      current_user.favorites << @recipe
      redirect_to :back, notice: 'You favorited #{@recipe.name}'

    elsif type == "unfavorite"
      current_user.favorites.delete(@recipe)
      redirect_to :back, notice: 'Unfavorited #{@recipe.name}'

    else
      # Type missing, nothing happens
      redirect_to :back, notice: 'Nothing happened.'
    end
  end

end

In your view you can then add the respective links to favoriting and unfavoriting recipes.

<% if current_user %>
  <%= link_to "favorite",   favorite_recipe_path(@recipe, type: "favorite"), method: :put %>
  <%= link_to "unfavorite", favorite_recipe_path(@recipe, type: "unfavorite"), method: :put %>
<% end %>

That's it. If a user clicks on the "favorite" link next to a recipe, this recipe is added to the current_user's favorites.

I hope that helps, and please ask any questions you like.

The Rails guides on associations are pretty comprehensives and will help you a lot when getting started.

Posted by Thomas Klemm at Implement "Add to favorites" in Rails 3 & 4 but I keep getting an error: uninitialized constant User::FavoriteRecipe

some help would be appreciated