Restful Nested Resources in Rails 2.0

There are several tutorials around for Rails 2.0 and nested resources (Akita, Adam Heroku). I wish I could get a hold of Adam's code files, but I keep getting 404 not found).


I struggled a lot and finally figured out how to do this right. I have been keeping a log of my own coding to share with my team, and these are my logging notes. Email me if you want the actual files, and I will be happy to share.

In my case, I have a parent 'user', that can own multiple children 'categories'.

Steps:
1> I use straight up scaffolding to generate the models, controllers, and migrations for User and Category. BTW, only later, reading Akita, did I discover the option of declaring "t.references :user" for the 'categories' migration. Interesting tid-bit that I did not know.
2> For the routes.rb, following Adam's path, I do not create a seperate category resource. I use the simple has_many declaration to denote that categories are children of user. Note that I am using the acts_as_authenticated plugin, and this had to come after all the other 'user' related declarations in the routes file.
map.resources :users, :has_many => :categories
3> In the User model, declare has_many :categories, and in Category model, declare belongs_to :user
4> Following Adam's instructions, type 'rake/routes', and let your eyes bleed over the keyboard. Try to look for the routes that give you the 'user_categories' like paths.
5> After this, Adam's examples become a little hard to follow, and I will try to spell out the next steps in gory detail. Hopefully, if will save some newbies like me a couple of hours.


6> Changes in the categories_controller.rb
6a> Start at the very bottom: Create a private method that loads the user from params:
6aa> private def load_user @usr = User.find(params[:user_id]) end
6ab> Then use this in a before_filter :load_user at the very top of the controller.
6b> For 'index' method, modify line 7: @categories = @user.categories.find(:all)
6c> No change in 'show'
6d> For new, @category = Category.new(:user_id => @user.id). Not sure this is absolutely necessary.
6e> No change in 'edit'
6f> For 'create'. @category = @user.categories.build(params[:category]). Note the new method 'build', working on the @user object.
6ff> The 'redirect' changes to format.html { redirect_to ([@user, @category]) }. Note that it is passing an array.
6g> In update, same 'redirect' change, format.html { redirect_to ([@user, @category]) }
6h> In 'destroy', redirect change, { redirect_to(user_categories_url(@user)) }

7> Changes in the 'index' view: Note how 'user' is prefixed to all 'category_path'
7a> 'Show' link: link_to 'Show', user_category_path(category.user, category)
7b> 'Edit' link: link_to 'Edit', edit_user_category_path(category.user, category)
7c> 'Delete' link: link_to 'Delete', user_category_path(category.user, category), :confirm => 'Are you sure?', :method => :delete

8> Changes in the 'new' view:
8a> form_for([@user, @category]) do f: Passing an array of the @user and @category objects
8b> Link 'back' to index: link_to 'Back', user_categories_path

9> Changes in the 'edit' view:
9a> form_for([@user, @category]) : Again, passing two objects in the form
9b> 'show' link needs 'user' in the path, as well as the two objects: link_to 'Show', user_category_path(@user, @category)
9c> 'back' link simply needs to put the 'user' prefix: link_to 'Back', user_categories_path

10> Changes in the 'show' view: Only @category object needed here. Changes are in the links
10a> 'edit' link: edit_user_category_path(@category.user, @category)
10b> 'back' link simply needs to put the 'user' prefix: link_to 'Back', user_categories_path

This is a lot of typing, and manual work. There should be a plugin for this, and sure enough, there is one (http://deaddeadgood.com/2008/10/8/scaffolding-nested-resources-in-rails). However, I am a Windows user, and have not yet discovered the joys of Git. That automatically puts you in Rails purgatory. I believe I am the only PC user who comes to our local ruby meetup. However, there is hope (http://jamie.ideasasylum.com/2008/08/installing-rails-plugins-with-git-on-windows/). Haven't tried this one out yet. I do think that it is not fair to impose this much pain on Windows users to just install plugins.

Fusion Charts with Ruby on Rails

Seasonality is an important component of forecasting, and thanks to Google Trends, we can quickly get multi-year seasonality for a category such as 'Turtlenecks'. After downloading the CSV file, I wanted to reproduce the chart from the data on our web-page.

Fusion Charts is a fantastic charting package, although so far we can only afford the free version. I will show a particular trick of extending Fusion Charts Free to manipulate the X-axis label. The time series from Google Trends had 234 weeks of data, which meant 234 labels. These ran into each other, creating an illegible axis. Also, the default mode for Fusion Charts is to display the values of the data points. With a lot of data points, these crowd the graph. The results, as seen here, are a far cry from the beautiful graphs of Google Trends.

A little bit of Ruby goes a long way to quickly fix this problem. First of all, I need to tell Fusion Charts to suppress the value on the graph. This is done by setting the showValues parameter to 0 in the xml header. I am using the excellent Builder library, where I can pass this as a key-value pair :showValues => 0. Next, I want to show the week for every 13th week. The paid version of Fusion Charts has a parameter setting for this. But for the cheapskates of the world, Ruby to the rescue again. The trick is to set the showName parameter to 0 in every thirteenth line of the xml. Finally, let's rotate the labels so they are vertically oriented, reducing the overlap. This is done by passing another key-value pair to the xml head, :rotateNames => 1. The final code to generate the xml is posted below. The new graph, after the changes, is much cleaner.

counter = 0

xml.graph (:showValues => 0, :rotateNames=> 1) do

@trend_weeks.each do tweek

counter = counter + 1

if counter.modulo(13) == 0 xml.set :name => tweek.week_date, :value => tweek.index

else

xml.set :name => tweek.week_date, :value => tweek.index, :showName => 0

end

end

end

I am still new to Ruby, and am sure there is a more idiomatic way of doing this. Please post it in the comments.

Also, it took me a very long time to get Fusion Charts to work the first time in Rails. It was mostly little mistakes that I kept making, as well as an incomplete understanding of how routes worked in the 2.0 world. I may get along to posting a full tutorial on this subject. If somebody needs to get started quickly, please contact me and I can try and help you. Happy Charting!

The Evolution of Analytics

Enterprises today are awash in data. POS systems capture every transaction for a retailer, CRM systems maintain rich profiles of customer preferences and ERP systems maintain transactional information at the most granular levels. Until the mid-nineties, only very large companies, the ones who could afford SAP or Oracle, could afford a reliable data infrastructure. However, even the large companies had to rely on smaller, niche players for analytical and optimization capabilities. The late nineties saw a number of companies starting to offer analytical products around supply chain optimization (i2, Manugistics). Soon, companies followed with Price Optimization, based on advanced scientific algorithms (ProfitLogic, DemandTec, etc.). Analytical evolution had come a long way: with Oracle, SAP, Teradata providing the data infrastructure, reporting vendors (Cognos, MicroStrategy) providing ad-hoc access to information and knowledge, and specialized vendors providing prescriptive modeling and optimization capabilities.

What has changed in the last couple of years is that high level data infrastructure is no longer limited to large companies. The giants like SAP are now catering to small and medium businesses (SMBs) with simpler offerings, and players like NetSuite are now providing extremely robust ERP systems as a hosted service. While data infrastructure is now available to the masses, science-based analytical software is still very expensive to build and distribute, and mostly beyond the SMB's price-range. SMBs are still lagging in the analytical evolution, although the appetite for analytical excellence is definitely palpable.

A combination of factors is changing this picture, giving SMBs access to high quality analytics at a price point that they can afford. The biggest contribution comes from the open-source community, in the form of relational databases (MySQL, PostGres), web-development frameworks (Ruby on Rails, Django), and optimization programs and solvers (COIN-OR, Scipy). Ruby on Rails makes it possible to go from a business meeting to a working application in a matter of weeks, not months or years. Amazon Web Services provides the physical infrastructure which allows running the complex algorithms on their compute clouds for less than a cup of coffee at Starbucks. As these innovations are driving the costs down, and enhancing the supply of high-quality analytics, the demand for these services are increasing as well. Enterprises large and small are becoming increasingly aware of the power of data and data-driven models, and seeking to gain competitive edge through analytics (Competing on Analytics).

The future centers of analytical excellence may be quite different from what we are used to today. Today's paradigm is niche analytical companies selling to large enterprises. The sales cycle is long and complex, licenses and implementation costs run in six figures, and hosting and maintenance are just as expensive. The future may be ruled by small, nimble shops, providing high-quality, low-cost intelligence over the web, in a simple Do It Yourself (DIY) mode. Are you ready for the brave new world of analytics?