Module: ActiveRecord::NamedScope::ClassMethods

Defined in:
lib/active_record/named_scope.rb

Instance Method Summary collapse

Instance Method Details

#named_scope(*args, &block) ⇒ Object 



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# File 'lib/active_record/named_scope.rb', line 123

def named_scope(*args, &block)
  ActiveSupport::Deprecation.warn("Base.named_scope has been deprecated, please use Base.scope instead", caller)
  scope(*args, &block)
end

#scope(name, scope_options = {}, &block) ⇒ Object

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



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# File '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

#scoped(options = nil) ⇒ Object

Returns an anonymous scope.

posts = Post.scoped
posts.size # Fires "select count(*) from  posts" and returns the count
posts.each {|p| puts p.name } # Fires "select * from posts" and loads post objects

fruits = Fruit.scoped
fruits = fruits.where(:colour => 'red') if options[:red_only]
fruits = fruits.limit(10) if limited?

Anonymous scopes tend to be useful when procedurally generating complex queries, where passing intermediate values (scopes) around as first-class objects is convenient.

You can define a scope that applies to all finders using ActiveRecord::Base.default_scope.



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# File 'lib/active_record/named_scope.rb', line 28

def scoped(options = nil)
  if options
    scoped.apply_finder_options(options)
  else
    current_scoped_methods ? relation.merge(current_scoped_methods) : relation.clone
  end
end

#scopes ⇒ Object 



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# File 'lib/active_record/named_scope.rb', line 36

def scopes
  read_inheritable_attribute(:scopes) || write_inheritable_attribute(:scopes, {})
end