Ordering records through index page record with AJAX (powered by jQuery) in a Ruby on Rails 3.1 App

_ordering.html.erb

<%#PATH: app/views/products/ %>
<% if !product.first? %>
  <%= link_to image_tag("ordering_icons/up.gif", :alt => "up", :title => "Move up"), move_up_product_path(product), :method => :put, :remote => true %>
<% end %>
<% if !product.last? %>
  <%= link_to image_tag("ordering_icons/down.gif", :alt => "down", :title => "Move down"), move_down_product_path(product), :method => :put, :remote => true %>
<% end %>

add_sort_index_to_products.rb

#PATH: db/migrate/

class AddSortIndexToProducts < ActiveRecord::Migration
  def self.up
    add_column :products, :sort_index, :integer
  end

  def self.down
    remove_column :products, :sort_index
  end
end

index.html.erb

<%#PATH: app/views/products/ %>

<h1>Products</h1>

<p><%= link_to "New Product", new_product_path %></p>

<table>
  <thead>
    <tr>
      <th></th>
      <th>Name</th>
      <th>Price</th>
    </tr>
  </thead>
  <tbody>
    <% @products.each do |product| %>
      <tr id="product_#{product.id}">
        <td id="product_#{product.id}_sort">
          <%= render :partial => "ordering", :locals => {:product => product} %>
        </td>
        <td><%= product.name %></td>
        <td><%= product.price %></td>
      </tr>
    <% end %>
  </tbody>
</thead>

move_down.js.erb

<%#PATH: app/views/products/ %>

$(function(){
    <% if @success %>
      $("#product_<%[email protected]%>").next().after($("#product_<%[email protected]%>"));
      $("#product_<%[email protected]%>_sort").html("<%= escape_javascript(render :partial => "ordering", :locals => {:product => @product} ) %>");
      $("#product_<%[email protected]%>_sort").html("<%= escape_javascript(render :partial => "ordering", :locals => {:product => @product.previous} ) %>");
    <% else %>
      alert("It wasn't possible to move the product. The last product can't be moved further down...")
    <% end %> 
  });

move_up.js.erb

<%#PATH: app/views/products/ %>

$(function(){
    <% if @success %>
      $("#product_<%[email protected]%>").prev().before($("#product_<%[email protected]%>"));
      $("#product_<%[email protected]%>_sort").html("<%= escape_javascript(render :partial => "ordering", :locals => {:product => @product} ) %>");
      $("#product_<%[email protected]%>_sort").html("<%= escape_javascript(render :partial => "ordering", :locals => {:product => @product.next} ) %>");
    <% else %>
      alert("It wasn't possible to move the product. The first product can't be moved further up...")
    <% end %>
  });

product.rb

#PATH: app/models/

class Product < ActiveRecord::Base

  attr_accessible :sort_index, :name, :price

  before_create :set_sort_index

  def last?
    self.sort_index == Product.maximum('sort_index')
  end

  def first?
    self.sort_index == 0
  end

  def next
    Product.where(:sort_index => (self.sort_index+1)).first
  end

  def previous
    Product.where(:sort_index => (self.sort_index-1)).first
  end

  def move_up
    switched = Product.where(:sort_index => (self.sort_index - 1)).first
    return false if !switched
    switched.sort_index = self.sort_index
    self.sort_index -= 1
    switched.save
    self.save
  end

  def move_down
    switched = Product.where(:sort_index => (self.sort_index + 1)).first
    return false if !switched
    switched.sort_index = self.sort_index
    self.sort_index += 1
    switched.save
    self.save
  end

  private

  def set_sort_index
    current_max_index = Product.maximum('sort_index') || -1
    self.sort_index = current_max_index+1
  end

end

product_ordering.rb

#PATH: spec/models/

require 'spec_helper'

describe 'setting and updating product sort_index value' do
  it "should set the sort_index value to zero for the first product, and then increment the sort_index value for the following records" do
    #no products 
    Product.all.count.should == 0

    #create a product 
    product = Product.create
    Product.all.count.should == 1
    product.sort_index.should == 0

    #create another product 
    product1 = Product.create
    Product.all.count.should == 2
    product1.sort_index.should == 1

    #create another product 
    product2 = Product.create
    Product.all.count.should == 3
    product2.sort_index.should == 2
  end

  it "should respond true to first? and last? if there's only a product and it has sort_index value of 0" do
    product = Product.create
    product.first?.should == true
    product.last?.should == true
    product.sort_index.should == 0
  end

  it "responds true to the method first? and false to the method last? when called on a product with sort_index 0, and when there is a second product with sort_index value 1" do
    product = Product.create
    product1 = Product.create
    product.first?.should == true
    product.last?.should == false
    product.sort_index.should == 0

    product1.first?.should == false
    product1.last?.should == true
    product1.sort_index.should == 1
  end

  it "responds false to both first? and last? when called on a product with sort_index 1, and there are other designations of the same level with sort_index 0 and 2" do
    product = Product.create
    product1 = Product.create
    product2 = Product.create

    product.first?.should == true
    product.last?.should == false
    product.sort_index.should == 0

    product1.first?.should == false
    product1.last?.should == false
    product1.sort_index.should == 1

    product2.first?.should == false
    product2.last?.should == true
    product2.sort_index.should == 2
  end

  it "should return the product with sort_index+1 when calling next on a product. it should return nil if there isn't another product" do
    product = Product.create
    product.next.should == nil
    product.previous.should == nil
    product1 = Product.create
    product.next.should == product1
    product1.sort_index.should == product.sort_index+1
    product1.previous.should == product
  end

  #Order hierarchy: 0, 1, 2, ...
  it "should increase the sort_index of a product when moving it down, and increase it when moving up, updating the other products accordingly" do
    product = Product.create
    product1 = Product.create
    product2 = Product.create

    product.sort_index.should == 0
    product1.sort_index.should == 1
    product2.sort_index.should == 2

    product.move_down
    product.reload
    product1.reload
    product2.reload
    product.sort_index.should == 1
    product1.sort_index.should == 0
    product2.sort_index.should == 2

    product.move_down
    product.reload
    product1.reload
    product2.reload
    product.sort_index.should == 2
    product1.sort_index.should == 0
    product2.sort_index.should == 1

    product.move_down
    product.reload
    product1.reload
    product2.reload
    product.sort_index.should == 2
    product1.sort_index.should == 0
    product2.sort_index.should == 1

    product.move_up
    product.reload
    product1.reload
    product2.reload
    product.sort_index.should == 1
    product1.sort_index.should == 0
    product2.sort_index.should == 2

    product.move_up
    product.reload
    product1.reload
    product2.reload
    product.sort_index.should == 0
    product1.sort_index.should == 1
    product2.sort_index.should == 2

    product.move_up
    product.reload
    product1.reload
    product2.reload
    product.sort_index.should == 0
    product1.sort_index.should == 1
    product2.sort_index.should == 2
  end
end

products_controller.rb

#PATH: app/controllers/

class ProductsController < ApplicationController

  respond_to :html, :js

  def index
    @products = Product.order("sort_index ASC")
  end

  def move_up
    @product = Product.find(params[:id])
    @success = [email protected]? && @product.move_up
  end

  def move_down
    @product = Product.find(params[:id])
    @success = [email protected]? && @product.move_down
  end
end

routes.rb

#PATH: config/

YourApplication::Application.routes.draw do

  resources :products do
    member do
      put :move_up
      put :move_down
    end
  end
end