Rails makes it easy to adapt Restful architecture. All you have to do is following.
1map.resources :pictures
I started putting all pictures related activities in pictures_controller.rb . In the beginning it was simple.
Slowly the application evolved. The application started handling two different types of pictures. There would be pictures for events and then there would be pictures of users using the system.
One can add comments to the event pictures but one can't add comment to user pictures. Slowly the requirement for event pictures grew vastly different from user pictures.
Sounds familiar. Right. Initially controller takes on a few responsibilities but slowly the controller starts taking a lot more responsibilities and then controller becomes huge.
The pictures controller was really huge and was fast becoming a mess and specially writing test was getting very difficult.
Time had come to create two different controllers: one for event pictures and one for user pictures.
But wait. Lots of people would say that if we want to be restful then there has to be one to one mapping between the model and the controller. Not true.
Model != resource
Being restful does not mean that there has be a one to one mapping between the model and the controller.
I am going to create a new controller called user_pictures_controller.rb which will take on all the functionality related to users dealing with picture. And this is going to be restful.
1map.resources :user_pictures
Above I have defined a resource called user_pictures. To keep it simple this controller would do only three things.
- display all the pictures of the user ( index )
- allow user to upload pictures ( create )
- allow user to delete a picture ( destroy )
That's the general idea. In my application I have only three actions.
However in the interest of general discussion I am going to show all the seven methods here. Also for simplicity create in this case means adding a record (I am not showing multipart upload).
Controller
Here is the code for controller.
1 2# user_pictures_controller.rb 3 4class UserPicturesController < ApplicationController 5 6 def index 7 @pictures = Picture.all 8 end 9 10 def new 11 render 12 end 13 14 def create 15 @picture = Picture.new(params[:picture]) 16 if @picture.save 17 flash[:notice] = 'Picture was successfully created.' 18 redirect_to user_picture_path(:id => @picture.id) 19 else 20 render :action => "new" 21 end 22 end 23 24 def show 25 @picture = Picture.find(params[:id]) 26 end 27 28 def edit 29 @picture = Picture.find(params[:id]) 30 end 31 32 def update 33 @picture = Picture.find(params[:id]) 34 if @picture.update_attributes(params[:picture]) 35 flash[:notice] = 'Picture was successfully updated.' 36 redirect_to user_picture_path(:id => @picture.id) 37 else 38 render :action => "edit" 39 end 40 end 41 42 def destroy 43 @picture = Picture.find(params[:id]) 44 @picture.destroy 45 46 redirect_to user_pictures_path 47 end 48 49end
View
1# index.html.erb 2<h1>Listing pictures</h1> 3 4<table> 5 <tr> 6 <th>Name</th> 7 <th>Quality</th> 8 </tr> 9 10<% for picture in @pictures %> 11 <tr> 12 <td><%=h picture.name %></td> 13 <td><%=h picture.quality %></td> 14 <td><%= link_to 'Show', user_picture_path(picture) %></td> 15 <td><%= link_to 'Edit', edit_user_picture_path(picture) %></td> 16 <td> <%= link_to 'Destroy', user_picture_path(picture), 17 :confirm => 'Are you sure?', 18 :method => :delete %> 19 20 </td> 21 </tr> 22<% end %> 23</table> 24 25 26<%= link_to 'New picture', new_user_picture_path %>
1# edit.html.erb 2<h1>Editing picture</h1> 3 4<% form_for(:picture, 5 :url => user_picture_path(@picture), 6 :html => {:method => :put}) do |f| %> 7 <%= f.error_messages %> 8 9 <p> 10 <%= f.label :name %><br /> 11 <%= f.text_field :name %> 12 </p> 13 <p> 14 <%= f.label :quality %><br /> 15 <%= f.text_field :quality %> 16 </p> 17 <p> 18 <%= f.submit "Update" %> 19 </p> 20<% end %> 21 22<%= link_to 'Show', user_picture_path(@picture) %> | 23<%= link_to 'All', user_pictures_path %>
1# new.html.erb 2<h1>New picture</h1> 3 4<% form_for(:picture, :url => user_pictures_path, :html => {:method => :post}) do |f| %> 5 <%= f.error_messages %> 6 7 <p> 8 <%= f.label :name %><br /> 9 <%= f.text_field :name %> 10 </p> 11 <p> 12 <%= f.label :quality %><br /> 13 <%= f.text_field :quality %> 14 </p> 15 <p> 16 <%= f.submit "Create" %> 17 </p> 18<% end %> 19 20<%= link_to 'All', user_pictures_path %> 21
1# show.html.erb 2<p> 3 <b>Name:</b> 4 <%=h @picture.name %> 5</p> 6 7<p> 8 <b>Quality:</b> 9 <%=h @picture.quality %> 10</p> 11 12<%= link_to 'Edit', edit_user_picture_path(:id => @picture) %> | 13<%= link_to 'All', user_pictures_path %>
Another use case
Let's talk about another example. Let's say that we have a model called Project and besides the regular functionality of creating, deleting, updating and listing projects, one needs two more actions called enable and disable project.
Well the projects controller can easily handle two more actions called "enable" and "disable". However it is a good idea to create another controller called project_status_controller . This controller should have only two actions - create and destroy. destroy in this case would mean disabling the project and create would mean enabling the project.
I know it looks counter intuitive. Actions 'enable' and 'disable' seem simpler than "create" and "destroy". I agree in the beginning adding more actions to pictures controller looks easy. However if we go down that path then it is a slippery slope and we do not know when to stop.
Compare that with the RESTful design of having only seven action : index, show, new, edit, create, update, destroy. This limits what a controller can do and that's a good thing. This ensures that a controller does not take up too many responsibilities.
Creating another controller allows all the business logic which is not related to one of those seven actions to be somewhere else.
One last example
Now that we have the ability to "enable" and "disable" pictures how about showing "only active", "only inactive" and "all" pictures.
In order to accomplish it once again we can add more actions to the pictures controller.
However it is much better to have two new controllers.
1class Pictures::ActiveController < ApplicationController 2end 3 4class Pictures::InactiveController < ApplicationController 5end
Some of you must be thinking what's the point of having a controller for the sake of having only one action. Well the point is having code that can be changed easily and with confidence.
Conclusion
In this blog I tried to show that it is not necessary to have one to one mapping between model and controllers to be restful. It is always a good idea to create a separate controller when the existing controller is burdened with too much work.