Module: ActiveRecord::Associations::ClassMethods

Defined in:
lib/activerecord_null_object.rb

Instance Method Summary collapse

Instance Method Details

#belongs_to_with_null_object(association_id, options = {}) ⇒ Object

Add a boolean :null_object option to belongs_to.



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# File 'lib/activerecord_null_object.rb', line 6

def belongs_to_with_null_object(association_id, options = {}) #:nodoc:
  # Extract our custom option.
  use_null_object = options.delete(:null_object)
  # Call the real belongs_to so that the association gets defined.
  belongs_to_without_null_object(association_id, options)
  # Modify the association if need be.
  if use_null_object
    
    # Determine the class of the association.
    association_class_name = options[:class_name] || association_id.to_s.classify
    association_class = association_class_name.constantize

    # Determine the null class for this association.
    null_class_name = "Null" + association_class_name
    if Object.const_defined?(null_class_name)
      null_class = Object.const_get(null_class_name.to_sym)
    else
      # Define the null class as an ancestor of the association class.
      null_class = Object.const_set(null_class_name, Class.new(association_class))
      null_class.class_eval do
        include Singleton
        include ActiveRecordNullObject::NullObject
      end
    end

    # Modify the "getter" of the belongs_to relationship to return an
    # instance of the association's null object instead of returning nil.
    class_eval do
      define_method("#{association_id}_with_null_object".to_sym) do
        send("#{association_id}_without_null_object".to_sym) || null_class.instance
      end
      alias_method_chain association_id, :null_object
    end
    
  end
end