Bits of Code #2 - Ordering records through index page with AJAX (powered by jQuery) in a Rails 3.1 App

In one of the projects that I worked in I had to make it possible for users to easily change the order in which the records of a table would appear in their index page. I knew that there were a few gems out there that could handle this for me, but I thought that it was such a simple functionality that it was probably not a strong enough reason to add another dependency to the project; so I went about building it.

In this example I've added this functionality to a Product model. I started by creating a migration to add the column that would keep the order between products, I decided to call this column sort_index.

	#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

view raw add_sort_index_to_products.rb hosted with ❤ by GitHub

Then I added a few methods to the Product model. Some methods to check the position of a product, others to move the product up and down in the 'ranking' of products, and a before_create callback to set the initial sort_index of each new product. Note that the upper position in my implementation is the position with sort_index equal to 0, so moving a product up is actually reducing its sort_index by 1.

	#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

view raw product.rb hosted with ❤ by GitHub

These methods were tested with RSpec (might not be 100% coverage, let me know if that is the case). I've moved the RSpec file to the end of the post because is quite a long file.

Having these methods working I implemented the functionality and the interface to allow the users to actually change the ordering of the products.

Created the necessary routes.

	#PATH: config/
	YourApplication::Application.routes.draw do
	resources :products do
	member do
	put :move_up
	put :move_down
	end
	end
	end

view raw routes.rb hosted with ❤ by GitHub

Created the controller methods.

	#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 = !@product.first? && @product.move_up
	end
	def move_down
	@product = Product.find(params[:id])
	@success = !@product.last? && @product.move_down
	end
	end

view raw products_controller.rb hosted with ❤ by GitHub

Followed by the views. The index page.

	<%#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>

view raw index.html.erb hosted with ❤ by GitHub

Which calls the _ordering partial

	<%#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 %>

view raw _ordering.html.erb hosted with ❤ by GitHub

And then the js views to process the result of the requests. To move down.

	<%#PATH: app/views/products/ %>
	$(function(){
	<% if @success %>
	$("#product_<%=@product.id%>").next().after($("#product_<%=@product.id%>"));
	$("#product_<%=@product.id%>_sort").html("<%= escape_javascript(render :partial => "ordering", :locals => {:product => @product} ) %>");
	$("#product_<%=@product.previous.id%>_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 %>
	});

view raw move_down.js.erb hosted with ❤ by GitHub

And to move up.

	<%#PATH: app/views/products/ %>
	$(function(){
	<% if @success %>
	$("#product_<%=@product.id%>").next().after($("#product_<%=@product.id%>"));
	$("#product_<%=@product.id%>_sort").html("<%= escape_javascript(render :partial => "ordering", :locals => {:product => @product} ) %>");
	$("#product_<%=@product.previous.id%>_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 %>
	});

view raw move_down.js.erb hosted with ❤ by GitHub

If you need to use this in more than one model you can move some bits into a Module and then include the Module where necessary. I haven't had the need to do it. But if I do, I'll probably do a post about it.

Hope these bits of code are useful for you some day, I've already used in two projects. If you find any issues or have any suggestions to improve this code please let me know.

And now for the RSpec file:

	#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

view raw product_ordering.rb hosted with ❤ by GitHub

Bits of Code - Nested Attributes

Yesterday I had the need to implement a form with some nested attributes and so I did what I often do: I went back to a previous project and copy&pasted the necessary code and then changed it to match the new project's needs.

While I was doing this I thought that it would be useful to get this, and other bits of code in a place that I can easily refer to, instead of having to remember in which project I've used what. This is the reasoning behind this post.

Bare in mind that this is not a post about life changing bits of code, but rather bits of code that I need now and then and that are easier to just copy&paste&edit than to have to rewrite from scratch. Some of these bits can be easily found in different websites, but having them here will make my life easier than having to search again. I'll make sure I'll refer to the websites that I've used.

So these first bits of code are meant to build a form with nested attributes.

Imagine that you have a model named Content that has many Attachments and when you are adding or editing a content, you want to be able to manage that content's attachments. This allows you to easily do it.

This code uses Rails accepts_nested_attributes_for and then it manages the different attachments with javascript methods (using jQuery framework), allowing you to add, remove and edit them accordingly.

The Content model:

	class Content < ActiveRecord::Base
	has_many :attachments
	accepts_nested_attributes_for :attachments, :allow_destroy => true
	end

view raw content.rb hosted with ❤ by GitHub

The Attachment model (notice the accepts_nested_attributes_for method):

	class Attachment < ActiveRecord::Base
	belongs_to :content
	end

view raw attachment.rb hosted with ❤ by GitHub

The ApplicationHelper, with the methods used in the views:

	module ApplicationHelper
	def link_to_remove_fields(name, f)
	f.hidden_field(:_destroy) + link_to_function(name, "remove_fields(this)", :class => "btn remove danger")
	end
	def link_to_add_fields(name, f, association)
	new_object = f.object.class.reflect_on_association(association).klass.new
	fields = f.fields_for(association, new_object, :child_index => "new_#{association}") do |builder|
	render(association.to_s.singularize + "_fields", :f => builder)
	end
	link_to_function(name, "add_fields(this, '#{association}', '#{escape_javascript(fields)}')", :class => "btn")
	end
	end

view raw application_helper.rb hosted with ❤ by GitHub

Part of the Content form view (notice the use of the method fields_for, and the helper method link_to_add_fields):

	<!-- other form code -->
	<div class="attachments">
	<%= f.fields_for :attachments do |attachment_form| %>
	<%= render 'attachment_fields', :f => attachment_form %>
	<% end %>
	</div>
	<%= link_to_add_fields "Attach a file or an image", f, :attachments %><br />
	<!-- other form code -->

view raw _form.html.erb hosted with ❤ by GitHub

The attachment_fields partial (notice the use of the helper method link_to_remove_field):

	<div class="attachment fields">
	<%= f.label :caption %>
	<%= f.file_field :document %>
	<%= link_to_remove_fields "remove", f %>
	</div>

view raw _attachment_fields.html.erb hosted with ❤ by GitHub

And the javascript methods (notice that if the position of the elements in the attachment_fields partial changes this code might need to be updated):

	function remove_fields(link) {
	$(link).prev("input[type=hidden]").val("1");
	$(link).closest(".fields").hide();
	}
	function add_fields(link, association, content) {
	var new_id = new Date().getTime();
	var regexp = new RegExp("new_" + association, "g")
	$("div.attachments").append(content.replace(regexp, new_id));
	}

view raw application.js hosted with ❤ by GitHub

 These bits of code are based on (or were copied from):

• Railscasts Nested Model Form - Part 1
• Railscasts Nested Model Form - Part 2
• Ryan's Scraps - What's new in Edge Rails - Nested Object Forms