association_joins.rb

module ActiveRecord
  module Associations
    module ClassMethods
      private
      @@valid_keys_for_belongs_to_association = [
        :class_name, :primary_key, :foreign_key, :foreign_type, :remote, :select, :conditions,
        :include, :dependent, :counter_cache, :extend, :polymorphic, :readonly, :joins, # added :joins key
        :validate, :touch
      ]
      @@valid_keys_for_has_many_association = [
        :class_name, :table_name, :foreign_key, :primary_key,
        :dependent,
        :select, :conditions, :include, :order, :group, :having, :limit, :offset, :joins, # added :joins key
        :as, :through, :source, :source_type,
        :uniq,
        :finder_sql, :counter_sql,
        :before_add, :after_add, :before_remove, :after_remove,
        :extend, :readonly,
        :validate
      ]
    end
  end
end