Module: WillPaginate::NamedScope::ClassMethods

Defined in:
lib/will_paginate/named_scope.rb

Instance Method Summary collapse

Instance Method Details

#named_scope(name, options = {}, &block) ⇒ Object

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, name scopes acts 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 were 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 descendent 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



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# File 'lib/will_paginate/named_scope.rb', line 79

def named_scope(name, options = {}, &block)
  scopes[name] = lambda do |parent_scope, *args|
    Scope.new(parent_scope, case options
      when Hash
        options
      when Proc
        options.call(*args)
    end, &block)
  end
  (class << self; self end).instance_eval do
    define_method name do |*args|
      scopes[name].call(self, *args)
    end
  end
end

#scopes ⇒ Object

:nodoc:



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# File 'lib/will_paginate/named_scope.rb', line 24

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