Question

This might be a noob question. But I couldn’t figure it out by myself.

In my application’ I’m using Rails 3.2.8 with Mongoid and MongoDB.

I have a instance variable like this:

ProgramsController < ApplicationController

@program = Program.find(params[:id])

In my view file, I need to use it many many times. For example;

@program.title
@program.content
@program.schedules (associated with Schedule model)
@program.articles (associated with Article model)

etc.

The issue is, I need to use that instance variable at DIFFERENT parts of the view. So it’s not something like doing a @program.each do |t| ....

BUT when ever I use @program at a different part of the view, that means a NEW query each time…

At the moment I have 31 queries for my view. Isn’t it too much?

So what is the best practice? How should I use instance variables effectively?

Thanks in advance.

Answer 1

Once the item has been stored in @program, it is indeed saved there and subsequent requests will not generate queries. If you only had references to @program.title and @program.content, you would probably be fine. Your issue is from the associations, like @program.schedules and @program.articles. The problem is that the schedules and articles are not being loaded from your @program = Program.find(params[:id]). This is referred to as the n+1 problem. The official docs state, under Eager Loading, that Eager loaded is supported on all relations with the exception of polymorphic belongs_to associations. and In order for eager loading to work, the Identity Map must be enabled.. If these two conditions are true, you should see a reduction in your queries. If you cannot accomodate those requirements, a good solution might be to do somethign like this in the controller, to grab them all ahead of time, in one query: @schedules = Schedule.find_by(program_id: @program.id)