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Nested Resources

• Create a Rails project named PetClinic with two scaffold-based controllers with model names Pet and Owner. Include owner_id (datatype integer) as one of the fields for Owner. This produces these entries in config/routes.rb:
  

  resources :pets     # (1)
  resources :owners   # (2)
  

  • The pets and owners are accessed with URLs similar to the sample URLs shown in the Scaffold Generated RESTful Routes Table.
     
  • In this case, every pet has an owner and every owner owns zero or more pets. This means that the owners and pets are in a one-to-many relationship.
     
  • Questions:
     
    
    1. How do you set up a one-to-many relationship between owners and pets?
        
    2. What does this relationship get for you?
        
    3. How could you test that this?
    
    
  • Because every owner owns a collection of pets, the pets resource is nested inside the owners resource. To configure pets as a resource nested inside of owners, change the resource declarations in (1) and (2) to
    

    resources :owners do
        resources :pets
    end
    

    • After making this change, the owners are still accessed as before because they are not nested in any other resource.
       
    • However, we should be able to access the pets according to their owners as shown in the Nested RESTful Routes Table. To show pet number 3 of owner 5, use this URL:
      

      http://localhost:3000/owners/5/pets/3
      

    • After making the change in #(3) to the routes file, the owner controller will work as before, but the Pets controller no longer works correctly. The remainder of this document describes the changes that must be made for pets to function as a nested resource within owners.
       
      
      1. Get the owner id from the route
          
         
         1. Enter this code at the bottom of the controller:
            

            private
            def get_owner
              @owner = Owner.find(params[:owner_id])
            end
            

             
         2. Invoke the get_owner method before anything else happens in the controller. Enter this code at the beginning of the controller:

            before_filter :get_owner
            

          
      2. Update the view routes.
          
         In the Pet views (index, show, new, edit), replace the scaffold-generated named routes in the first table by the named nested routes in the second table.
          
          
      3. Update the find statements in the Pets controller.
          
         Because the pets are nested within owners, we don't want all pets; we want only the pets that belong to the owner with id=owner_id.
          
         
         1. In the index method, replace
            

            @pets = Pet.find(:all)
            

            by
            

            @pets = @owner.pets
            

         2. In the show, edit, update, destroy methods, replace
            

            @pet = Pet.find(params[:id])
            

            by
            

            @pet = @owner.pets.find(params[:id])
            

            
            
         3. In the new method, replace
            

            @pet = Pet.new
            

            by
            

            @pet = @owner.pets.build 
            

         4. In the create method, replace
            

            @pet = Pet.new(params[:pet])
            

            by
            

            @pet = @owner.pets.build(params[:pet]) 
            

             
      4. Update the form_for statement
          
         In _form.html.erb, replace the @pet object in the form_for statement by the array [@owner, @pet].
          
          
      5. Update the redirect URLs in the controller.
          
         In the Pet controller, replace the scaffold-generated named routes in the first table by the named nested routes in the second table.
          

     

    Practice Problems

    1. On the show view for pets, replace Name: Coco (if it is a pet), by an h2 heading like this:

       Information for the Pet Named Coco

       Don't hardcode the name. The view should work for any owner.
        
    2. Repeat Problem 1 for the show view for owners.
        
    3. On the index view for owners, add a column that shows the pet count for each owner.
        
    4. On the show view for an owner, add a table that shows all of the pets for that owner.
        
    5. On the index view for pets, change the header to include the owners name. Remove the owner column in the table of pet information.
        
    6. On the show view for a pet, change the owner index to the owner name. Move the name of the pet to the header.
        
    7. Add hyperlinks on the pets views to permit navigation back to the owner views.
        
    8. Modify the CSS stylesheet for the project to allow more space between table rows and columns.
        
    9. Add a background image that will be applied to all views in the project.