Favorites model for my rails app

Question

I have a user and guideline model.

I would like a user to be able to mark a guideline as their favourite and then view a list of all their favourite guidelines.

It's not quite right. I'm not sure if the 'favourite' action is adding a favourite correctly; or if it is adding correctly it's not displaying correctly in the favourites view (so 'show' action may not be right)...

* CONTROLLER *guidelines_controller.rb

def favourite
   type = params[:type]
   if type == "favourite"
    @guideline= Guideline.find_all_by_id(params[:guideline_id])
    current_user.favourite_guidelines << @guideline
     redirect_to :back, notice: 'You favourited #{@guideline.name}'
    elsif type == "unfavourite"
     current_user.favourite_guidelines.delete(@guideline)
     redirect_to :back, notice: 'Unfavourited #{@guideline.name}'

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

* CONTROLLER *favourites_controller.rb

 def show

    @user = User.find_by_profile_name(params[:id])
    if @user 
        @guidelines = @user.favourite_guidelines.all
        render action: :show
    else
        render file: 'public/404', status: 404, formats: [:html]
    end
  end
end

* ROUTES *routes.rb

get "guidelines/favourite"
  get "favourites/show"

* MODEL *user.rb

has_many :guidelines
 has_many :favourite_guidelines

* MODEL *favourite_guidelines.rb

  attr_accessible :guideline_id, :user_id

  belongs_to :user

* VIEWS *guidelines/index.html.erb

<% if current_user %>
    <%= link_to "favourite",   guidelines_favourite_path(guideline, type: "favourite"), method: "get" %>
    <%= link_to "unfavourite", guidelines_favourite_path(guideline, type: "unfavourite"), method: "get" %>

* VIEWS *favourites/show.html.erb

<% if @guidelines %>
    <% @guidelines.each do |guideline| %>

        <div class="well">
            <%= link_to guideline.title, guideline %>
            <br />
            <%= guideline.content %>
            <br />
            Added <%=  time_ago_in_words(guideline.created_at) %> ago
        </div>
    <% end %>
<% end %>

Answer 1

As per your comment following returns nil :

@guideline= Guideline.find_by_id(params[:guideline_id])  #=> nil
current_user.favourite_guidelines << nil #Gives association mismatch error 

I think params[:guideline_id] is nil . Post your params from log file.

Or try this:

Change your link to like this:

<%= link_to "favourite",   guidelines_favourite_path(guideline_id: guideline.id, type: "favourite"), method: "get" %>
<%= link_to "unfavourite", guidelines_favourite_path(guideline_id: guideline.id, type: "unfavourite"), method: "get" %>

In your earlier case:

 @guideline= Guideline.find_all_by_id(params[:guideline_id]) #=> []
 current_user.favourite_guidelines << [] #=> Valid and inserting nothing