Object does not get loaded

Question

This is the weirdest thing ever happened to me with ruby/rails.

I have a model, Store, which has_many Balances. And I have a method that gives me the default balance based on the store's currency.

Store model.

class Store < ActiveRecord::Base

  has_many :balances, as: :balanceable, dependent: :destroy

  def default_balance
    #puts self.inspect <- weird part.
    balances.where(currency: self.currency)[0]
  end
  ...
end

Balance model.

class Balance < ActiveRecord::Base

  belongs_to :balanceable, :polymorphic => true
  ...
end

Ok, so then in the Balance controller I have the show action, that will give me a specific balance or the default one.

Balance controller.

class Api::Stores::BalancesController < Api::Stores::BaseController

  before_filter :load_store

  # Returns a specific alert
  # +URL+:: GET /api/stores/:store_id/balances/:id
  def show
    #puts @store.inspect <- weird part.
    @balance = (params[:id] == "default") ? @store.default_balance : Balance.find(params[:id])
    respond_with @balance, :api_template => :default
  end
  ...

  private
    # Provides a shortcut to access the current store
    def load_store
      @store = Store.find(params[:store_id])
      authorize! :manage, @store
    end
end

Now here is where the weird part comes...

If I make a call to the show action; for example:

GET /api/stores/148/balances/default

It returns null (because the currency was set as null, and there is no Balance with null currency), and the SQL query generated is:

SELECT `balances`.* FROM `balances` WHERE `balances`.`balanceable_id` = 148 AND `balances`.`balanceable_type` = 'Store' AND `balances`.`currency` IS NULL

So I DON'T know why... it is setting the currency as NULL. BUT if in any where in that process I put

puts @store.inspect

or inside the default_balance method:

puts self.inspect

it magically works!!!.

So I don't know why is that happening?... It seems like the store object is not getting loaded until I "inspect" it or something like that.

Thanks

Answer 1

Sam and Adrien are on the right path.

ActiveRecord overrides method_missing to add a whole bunch of dynamic methods including the accessors for the column-backed attributes like Store#currency. While I'm glossing over a lot, suffice it to say that when the logic is invoked then the dynamic class/instance methods are added to the Store class/instances so that subsequent calls no longer require the method_missing hook.

When YOU overrode method_missing without calling super, you effectively disabled this functionality. Fortunately, this functionality can be invoked by other means, one of which you tripped upon when you called store#inspect.

By adding the call to super, you simply assured that ActiveRecord's dynamic methods are always added to the class when they're needed.