Module: ActiveRecord::NamedScope::ClassMethods

Module | ActiveRecord::NamedScope::ClassMethods
In: | lib/active_record/named_scope.rb

### Methods

named_scope scopes

### Public Instance methods

named_scope(name, options = {}, &block)

Adds a class method for retrieving and querying objects. A scope represents a narrowing of a database query, such as `:conditions => {:color => :red}, :select => ‘shirts.*’, :include => :washing_instructions`.

      class Shirt < ActiveRecord::Base
        named_scope :red, :conditions => {:color => 'red'}
        named_scope :dry_clean_only, :joins => :washing_instructions, :conditions => ['washing_instructions.dry_clean_only = ?', true]
      end

The above calls to `named_scope` define class methods Shirt.red and Shirt.dry_clean_only. Shirt.red, in effect, represents the query `Shirt.find(:all, :conditions => {:color => ‘red’})`.

Unlike `Shirt.find(...)`, however, the object returned by Shirt.red is not an Array; it resembles the association object constructed by a `has_many` declaration. For instance, you can invoke `Shirt.red.find(:first)`, `Shirt.red.count`, `Shirt.red.find(:all, :conditions => {:size => ‘small’})`. Also, just as with the association objects, named \scopes act like an Array, implementing Enumerable; `Shirt.red.each(&block)`, `Shirt.red.first`, and `Shirt.red.inject(memo, &block)` all behave as if Shirt.red really was an Array.

These named \scopes are composable. For instance, `Shirt.red.dry_clean_only` will produce all shirts that are both red and dry clean only. Nested finds and calculations also work with these compositions: `Shirt.red.dry_clean_only.count` returns the number of garments for which these criteria obtain. Similarly with `Shirt.red.dry_clean_only.average(:thread_count)`.

All \scopes are available as class methods on the ActiveRecord::Base descendant upon which the \scopes were defined. But they are also available to `has_many` associations. If,

      class Person < ActiveRecord::Base
        has_many :shirts
      end

then `elton.shirts.red.dry_clean_only` will return all of Elton‘s red, dry clean only shirts.

Named \scopes can also be procedural:

      class Shirt < ActiveRecord::Base
        named_scope :colored, lambda { |color|
          { :conditions => { :color => color } }
        }
      end

In this example, `Shirt.colored(‘puce’)` finds all puce shirts.

Named \scopes can also have extensions, just as with `has_many` declarations:

      class Shirt < ActiveRecord::Base
        named_scope :red, :conditions => {:color => 'red'} do
          def dom_id
            'red_shirts'
          end
        end
      end

For testing complex named \scopes, you can examine the scoping options using the `proxy_options` method on the proxy itself.

      class Shirt < ActiveRecord::Base
        named_scope :colored, lambda { |color|
          { :conditions => { :color => color } }
        }
      end

      expected_options = { :conditions => { :colored => 'red' } }
      assert_equal expected_options, Shirt.colored('red').proxy_options

scopes()

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