Automatic Records Search in Rails

There is one neat trick I'd like to share. In many cases, especially when you work on intranet applications, you need say to check some security settings against the data-records before you let the request to access the actual method in your controller. Normally, most folks do that by adding before filters to find the records, like that

before_filter :find_this
before_filter :find_that

def find_this
def find_that

When your application grows and starts having something like a dozen models, plus you might have nested routes where you need to check the security against the nested elements too, those things tend to get really messy.

So here is a simple method which I use on my projects

before_filter :find_restful_units
def find_restful_units
  params.each do |key, value|
    if key == 'id' || key.ends_with?('_id')
      unit_name = key == 'id' ? controller_name.singularize : key.gsub('_id', '')
      unit_class = Object.const_get(unit_name.camelize)
      instance_variable_set("@#{unit_name}", unit_class.find(params[key]))
    end
  end

rescue NameError  # just hung up if there is no such unit
  nil
end

You put this in your ApplicationController and it will automatically find and assign all your models, the actual and the nested ones.

This makes controllers much cleaner and you always have your models extracted and ready to use in the standard way.