scope(name, scope_options = {}, &block) — ActiveRecord::NamedScope::ClassMethods

scope(name, scope_options = {}, &block)

Adds a class method for retrieving and querying objects. A \scope represents a narrowing of a database query, such as where(:color => :red).select('shirts.*').includes(:washing_instructions).

class Shirt < ActiveRecord::Base
  scope :red, where(:color => 'red')
  scope :dry_clean_only, joins(:washing_instructions).where('washing_instructions.dry_clean_only = ?', true)
end

The above calls to scope define class methods Shirt.red and Shirt.dry_clean_only. Shirt.red, in effect, represents the query Shirt.where(: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.first, Shirt.red.count, Shirt.red.where(: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
  scope :colored, lambda {|color| where(: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
  scope :red, where(:color => 'red') do
    def dom_id
      'red_shirts'
    end
  end
end

Scopes can also be used while creating/building a record.

class Article < ActiveRecord::Base
  scope :published, where(:published => true)
end

Article.published.new.published    # => true
Article.published.create.published # => true

Parameters

name req
scope_options opt = {}
block block

Source

# File activerecord/lib/active_record/named_scope.rb, line 100
      def scope(name, scope_options = {}, &block)
        name = name.to_sym
        valid_scope_name?(name)

        extension = Module.new(&block) if block_given?

        scopes[name] = lambda do |*args|
          options = scope_options.is_a?(Proc) ? scope_options.call(*args) : scope_options

          relation = if options.is_a?(Hash)
            scoped.apply_finder_options(options)
          elsif options
            scoped.merge(options)
          else
            scoped
          end

          extension ? relation.extending(extension) : relation
        end

        singleton_class.send(:redefine_method, name, &scopes[name])
      end

Defined in activerecord/lib/active_record/named_scope.rb line 100 · View on GitHub · Improve this page · Find usages on GitHub

Defined in ActiveRecord::NamedScope::ClassMethods

Signature

Parameters