Simply on Rails - Part 3: LiteController

Posted by h3rald Sun, 22 Jul 2007 12:03:00 GMT

Enough with concepts, ideas and diagrams: it’s time to start coding something. Everyone knows what’s the first step when creating a Rails applications, but anyhow, here it is:

rails italysimply

Then I create a new development database, load it up with the schema I previously prepared and modify the config/database.yml to be able to connect to it. Nothing new here. I actually had to modify the schema a little bit:

  • I changed all the names for the foreign keys to something more evocative than “has_many” or “has_one”
  • I added a level column to the states, availabilities and conditions table
  • I removed the description column from the categories table

Great, but… hang on: now some of the database tables look awfully similar with each other:

  • statuses
  • states
  • roles
  • types
  • tags
  • conditions
  • availabilities
  • categories

They all have a name column, some of them have a name column as well, they’ll hold only a relative small number of records which will hardly ever be deleted. In fact, I was tempted to use Enums for some of those things… Anyhow, I’ll still have to add and modify data in those tables, so it looks like I kinda need to create 8 controllers, 8 models and about four views for each one of them. No way. Fair enough for the controllers and models, but I’m not going to create 32 views which all look exactly the same. Rails should be smarter than that!

And it is, luckily. Derek Sivers & C. came out with an interesting Shared Controller concept, which could be just what I’m looking for in this case. Actually I need something really simple in this case:

  • Put all the CRUD logic into one controller
  • Create only one set of views

Here’s the controller:

app/controllers/admin/lite_controller.rb 
class Admin::LiteController < ApplicationController

  layout 'admin'

  before_filter :prepare

  def prepare
    @item_name = model.to_s
  end

  def index
    list
  end

  verify :method => :post, :only => [ :destroy, :create, :update ],
         :redirect_to => { :action => :list }

  def list
    ordering = model.column_names.include?('level') ? 'level ASC' : 'name ASC'
    @items = model.find(:all, :order => ordering)  
    render('lite/list')
  end

  def show
    @item = model.find(params[:id])
    render('lite/show')
  end

  def new
    @item = model.new
    render('lite/new')
  end

  def create
    @item = model.new(params[:"#{@item_name.downcase}"])
    if @item.save
      flash[:notice] = @item_name+' was successfully created.'
      redirect_to :action => 'list'
    else
      render('lite/new')
    end
  end

  def edit
    @item = model.find(params[:id])
    render('lite/edit')
  end

  def update
     @item = model.find(params[:id])
    if @item.update_attributes(params[:"#{@item_name.downcase}"])
      flash[:notice] = @item_name+' was successfully updated.'
      redirect_to :action => 'list'
    else
      render('lite/edit')
    end
  end
end

Then all I need to do is create eight controllers with just a few lines of code in each:

app/controllers/admin/statuses_controller.rb 
class Admin::StatusesController < Admin::LiteController
  def model
    Status
  end
end

Basically, I just need to specify which model the specific controller takes care of, Ruby’s inheritance does the rest. The model name will be passed to the views like this:

app/controllers/admin/lite_controller.rb 
def prepare
    @item_name = model.to_s
end

And each method uses the model method to access the model, like this:

app/controllers/admin/lite_controller.rb 
def create
    @item = model.new(params[:"#{@item_name.downcase}"])
    if @item.save
        flash[:notice] = @item_name+' was successfully created.'
        redirect_to :action => 'list'
    else
        render('lite/new')
    end
end

Note how the params are collected:

@item = model.new(params[:"#{@item_name.downcase}"])

params[:"#{@item_name.downcase}"] at runtime becomes params[:status] or params[:role] etc. etc., depending on which controller is called. Sweet.

The views? Modified accordingly:

app/views/lite/edit.rb 
<h1>Editing <%= @item_name %></h1>

<% form_tag :action => 'update', :id => @item do %>
  <%= render :partial => 'lite/form' %>
  <%= submit_tag 'Edit' %>
<% end %>

<%= link_to 'Show', :action => 'show', :id => @item %> |
<%= link_to 'Back', :action => 'list' %>
app/views/lite/_form.rb 
<%= error_messages_for 'item' %>
<!--[form:lite]-->
<p><label for="<%= @item_name.downcase %>_name">Name: </label>
<%= text_field @item_name.downcase, 'name',  {:value => @item.name} %></p>
<% if @item.methods.include?('level') then %> 
  <p><label for="<%= @item_name.downcase %>_level">Level: </label>
  <%= text_field @item_name.downcase, 'level',  {:value => @item.level} %></p>
<% end %>
<!--[eoform:lite]-->

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Leave a response

  1. Aleksandr said about 1 month later:

    Why aren’t you using REST?

  2. Fabio Cevasco said about 1 month later:

    @Aleksandr:

    Good question!

    The answer is that being it my first project in Rails, I was still a bit unsure about REST.

    On a side note, I’m currently considering using ActiveScaffold for things like this now… Will blog about it soon-ish.

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