How to use common named_scope for all ActiveRecord models

Hi how to build a named_scope which will be common for all mod开发者_如何学编程els.

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.

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.

For a Rails4 project I achieved this by extending ActiveRecord::Base, the class all Rails models inherit from, in an initializer (monkey patching approach, beware)

# in /config/initializers/shared_scope_initializer.rb
module SharedScopes
  extend ActiveSupport::Concern

  module ClassMethods
    def named_scope
      return where(attribute: value) # query here
    end
  end
end

ActiveRecord::Base.send(:include, SharedScopes)