require 'active_support/core_ext/array' require 'active_support/core_ext/hash/except' require 'active_support/core_ext/kernel/singleton_class' module ActiveRecord # = Active Record \Named \Scopes module Scoping module Named extend ActiveSupport::Concern module ClassMethods # Returns an ActiveRecord::Relation scope object. # # posts = Post.all # 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.all # fruits = fruits.where(color: 'red') if options[:red_only] # fruits = fruits.limit(10) if limited? # # You can define a scope that applies to all finders using # ActiveRecord::Base.default_scope. def all if current_scope current_scope.clone else default_scoped end end def default_scoped # :nodoc: relation.merge(build_default_scope) end # Collects attributes from scopes that should be applied when creating # an AR instance for the particular class this is called on. def scope_attributes # :nodoc: all.scope_for_create end # Are there default attributes associated with this scope? def scope_attributes? # :nodoc: current_scope || default_scopes.any? end # 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'). # # You should always pass a callable object to the scopes defined # with +scope+. This ensures that the scope is re-evaluated each # time it is called. # # Note that this is simply 'syntactic sugar' for defining an actual # class method: # # class Shirt < ActiveRecord::Base # def self.red # where(color: 'red') # end # end # # 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 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 # # \Class methods on your model are automatically available # on scopes. Assuming the following setup: # # class Article < ActiveRecord::Base # scope :published, -> { where(published: true) } # scope :featured, -> { where(featured: true) } # # def self.latest_article # order('published_at desc').first # end # # def self.titles # pluck(:title) # end # end # # We are able to call the methods like this: # # Article.published.featured.latest_article # Article.featured.titles def scope(name, body, &block) extension = Module.new(&block) if block singleton_class.send(:define_method, name) do |*args| if body.respond_to?(:call) scope = all.scoping { body.call(*args) } scope = scope.extending(extension) if extension else scope = body end scope || all end end end end end end