Question

Using Rails 3.1, I have the following:

# state.rb
class State < ActiveRecord::Base
  belongs_to :country, :touch => true

  after_save :count_total_states

  private

  def count_total_states
    total_states = State.where(:country_id => self.country_id).count
    Country.where(:id => self.country_id).update_column(:state, total_states)
  end
end

# states_controller.rb
class StatesController < ApplicationController
  def create
    @country = Country.find(params[:country_id])
    @state = @country.states.build(params[:state])
    @state.position = State.where(:country_id => @country.id).maximum(:position).to_i + 1
    @state.save
  end
end

When I create a new object for state, the following error shows:

NoMethodError in StatesController#create

undefined method `update_column' for #<ActiveRecord::Relation:0x1074b0e58>

What is the method going back to the controller? Please advise.

Thanks.

Answer 1

This error is because this:

Country.where(:id => self.country_id)

returns an ActiveRecord::Relation object, not a Country. You probably should do one of these two things instead:

Country.find(self.country_id).update_column(:state, total_states)

or

Country.where(:id => self.country_id).first.update_column(:state, total_states)

However I would recommend the first option because it does what you really want, finds a record by the ID. Using Where with a primary key is kind of funky, your objective is to return just one exact match and you know its ID so you should just grab it directly.

---

Note: I would also recommend update_attribute instead of update_column, as update_column skips all validation. It’s a good idea to validate unless you really can’t.

Better yet, the behavior you’re using is actually encapsulated into a standard Rails practice called “counter cache”. See this blog post and this Railscast for a demonstration of a better way to achieve your goal.