Question

We have a model association that looks something like this:

class Example < ActiveRecord::Base
  has_many :others, :order => 'others.rank'
end

The rank column is an integer type. The details of these particular models are not really important though as we have found the same problem with other has_many associations between other models.

We have also added to the Enumerable module:

module Enumerable
  def method_missing(name)
    super unless name.to_s[0..7] == 'collect_'
    method = name.to_s[8..-1]
    collect{|element| element.send(method)}
  end
end

This adds a collect_id method that we can use to get an array of record ids from an array of ActiveRecord objects.

So if we use a normal ActiveRecord find :all, we get a nice array which we can then use collect_id on but if we use Example.others.collect_id, we get

NoMethodError: undefined method `collect_id' for #<Class:0x2aaaac0060a0>

Example.others.class returns “Array” so is it lying or confused?

Our solution thus far has been to use it this way:

Example.others.to_a.collect_id 

This works but this seems a bit strange. Why would you have to do that?

We are on Ruby 1.8.7 and Rails 2.3.4

Answer 1

Model associations are proxies, not just simple Arrays.

Instead of example.others.all.collect_id and your patch, I suggest you use example.others.all.map(&:id) which is the standard Rails and Ruby >=1.8.7 way to collect a single attribute.