How to use common named_scope for all ActiveRecord models

Question

Hi how to build a named_scope which will be common for all models.

Answer 1

I do that by putting this code in lib/has_common_named_scopes.rb:

module HasCommonNamedScopes
  def self.included(base)
    base.class_eval {
      # Named scopes
      named_scope :newest, :order => "#{base.table_name}.created_at DESC"
      named_scope :freshest, :order => "#{base.table_name}.updated_at DESC"
      named_scope :limit, lambda { |limit| {:limit => limit} }
    }
  end
end

and then include the module in each model where I need them:

class MyModel < ActiveRecord::Base
  include HasCommonNamedScopes

I'd recommend that you use base.table_name to qualify the table when referring to columns in these named scopes like I do in the example. Otherwise you run into problems with ambiguous references when you combine these named scopes with other scopes that join in other tables.

Update:

scope is used in Rails > 3 and named_scope was used in previous versions.

Answer 2

There's also Thoughtbot's Pacecar, which adds a bunch of very common named scopes to every model. It might come with what you're looking for. If you need something custom, though, Casper Fabricius has the right idea.