多态和has_one关联

Question

I have set up a polymorphic association in my app. A picture belongs to both a scoreboard model and a user model as pictureable. Each scoreboard and user has_one picture. I also have nested routes where pictures resource is nested inside a user and scoreboard resource.

Routes File for the users:

resources :users do
  resources :picture
end

resources :account_activations, only: [:edit]
resources :password_resets, only: [:new, :create, :edit, :update]

resources :conversations, only: [:index, :show, :destroy] do
  member do
    post :reply
    post :restore
    post :mark_as_read
  end

  collection do
    delete :empty_trash
  end
end

Routes file for the scoreboard:

resources :scoreboards do 
  member do
    put :favourite
    get :deleteteams
    get :deleteschedules
  end

  resources :invitations, only: [:new, :create]
  resources :comments
  resources :teams, only: [:edit, :create, :destroy, :update]
  resources :schedules 
  resources :picture
end

I have setup a picture controller. The code is given below.

class PictureController < ApplicationController
  before_filter :load_pictureable

  def new 
    @picture = @pictureable.build_picture                              
  end                                               

  def create
  end

  def destroy
  end

  private

  def picture_params
    params.require(:picture).permit(:picture)
  end

  def load_pictureable
    klass = [User, Scoreboard].detect { |c| params["#{c.name.underscore}_id"] }
    @pictureable = klass.find(params["#{klass.name.underscore}_id"]) 
  end
end                           

My new form is given below:

 <div id= "uploadphoto">
   <%= form_for([@pictureable, @picture], url: scoreboard_picture_path, html: {multipart: true}) do |f| %>
     <%= f.file_field :picture, accept: 'image/jpeg,image/gif,image/png', id: "files", class: "hidden" %>
     <label for="files" id="picture"><h4 id="picturetext">Click Here to Upload Picture</h4></label>
       <div class="modal" id="modal-1">
         <div class="modal-dialog">
           <div class="modal-content">
             <div class="modal-header">Position and Crop your Image</div>
             <div class="modal-body">
               <div class="upload-preview">
                <img id="image" /></img>
               </div>
               <%= f.submit "upload photo" %>
             </div>
           <div class="modal-footer"> Click Anywhere Outside the box to Cancel</div>
         </div>
       </div>
     </div>
  <% end %>
</div>

The problem I am having is with the URL. This gives me the following error.

No route matches {:action=>"show", :controller=>"picture", :scoreboard_id=>"13"} missing required keys: [:id]

I am not sure why it redirects me to the show action, I assume its probably the nested routes.I don't know what the problem is. I thought I had resolved it by passing the following URL new_scoreboard_picture_path . However, when I press upload photo, It would take me back to the same URL. This makes sense because I am explicitly stating the URL in the new form. However, that is incorrect. It would be a great help if someone could help me figure out what the issue is. I have only included the relevant code. However, if i am missing anything please do let me know. Any explanation as to why I am getting this error would also clarify my though process. This is the first time working with polymorphic associations. Any sort of help would be great!!

Answer 1

I would use inheritance and two separate controllers instead:

# the base controller
class PicturesController < ApplicationController
  before_action :load_pictureable

  def new 
    @picture = @pictureable.build_picture                              
  end                                               

  def create
    @picture = @pictureable.build_picture
    if @picture.save
      do_redirect
    else
      render_errors
    end
  end

  def destroy
    # ...
  end

  private

  def picture_params
    params.require(:picture).permit(:picture)
  end

  # Finds the picturable based on the module name of the class
  # for examples `Pets::PicturesController` will look for
  # Pet.find(params[:pet_id])
  def find_pictureable
    # this looks at the class name and extracts the module name
    model_name = self.class.deconstantize.singularize
    @pictureable = model_name.constanize.find(params["#{model_name}_id"])
  end

  # subclasses can override this to whatever they want
  def do_redirect
    redirect_to @pictureable
  end

  # subclasses can override this to whatever they want
  def render_errors
    render :new
  end
end

Then setup the routes:

resources :users do
  resource :picture, controller: 'users/pictures'
end

resources :scoreboards do
  resource :picture, controller: 'scoreboards/pictures'
end

Since a user/scoreboard can have only one picture we are using resource and not resources . This sets up the routes for singular resource. Use rake routes to see the difference for yourself. For example you create a picture with POST /users/:user_id/picture .

We then setup the child controllers:

# app/controllers/users/pictures_controller.rb
class Users::PicturesController < PicturesController
end

 # app/controllers/scoreboards/pictures_controller.rb
class Scoreboards::PicturesController < PicturesController
end

This allows a high degree of customization without a jumble of if/else or switch statements. Also this safeguards against a malicious user passing params[:user_id] to manipulate a users picture. You should never use user input to determine classes or database tables.

Also you do not need to explicitly specify the form url:

<%= form_for([@pictureable, @picture], html: {multipart: true}) do |f| %>

Will use users_picture_path(user_id: @pictureable.id) or the same for scoreboards.

• http://guides.rubyonrails.org/routing.html#singular-resources
• http://api.rubyonrails.org/classes/ActionDispatch/Routing/PolymorphicRoutes.html