Ruby on Rails: Instantiate associated models with find_by_sql?

Question

Apparently, include and select can't be used simultaneously on a Rails find query, and this has been repeatedly marked as wontfix:
http://dev.rubyonrails.org/ticket/7147
http://dev.rubyonrails.org/ticket/5371

This strikes me as very inconvenient, because the times I'd want to use include are exactly the same times I'd want to use select - when every bit of performance counts.

Is there any way to work around this and manually generate a combined include-with-select using find_by_sql, or any other method? The trouble is, I'm not aware of any way to emulate the functionality of include, where it instantiates models in memory to hold the included associated models, such that I can enter model1.associated_models and have it not hit the database again.

Answer 1

Have you considered creating model for database view? For example:

• Create database view, with your complicated SQL query:

  CREATE VIEW production_plan_items AS
      SELECT * FROM [...]
      INNER JOIN [...];
  

• Create model for this view:

  # app/view_model.rb
  class ViewModel < ActiveRecord::Base
    self.abstract_class = true
  
    def readonly?
      true
    end   
  
    def before_destroy
      raise ActiveRecord::ReadOnlyRecord
    end 
  end
  
  # app/models/logical/production_plan_item.rb
  module Logical
    class ProductionPlanItem < ::ViewModel
    end
  end
  

• Use as always, but remember that these records are READ ONLY!

  Logical::ProductionPlanItem.where( ... )
  

If performance still be an issue in the future, you can quite easily convert DB views to materialized views using triggers and stored procedures. This will give your application enormous speed boost, and you don't have to change even one line of Rails code.

Enterprise Rails is highly recommended reading: http://www.amazon.com/Enterprise-Rails-Dan-Chak/dp/0596515200/ref=sr_1_1?ie=UTF8&qid=1293140116&sr=8-1