I Can Haz Scope?

Ruby on Rails: the scope method

Transcript

1. Model cat Model cat Ellen Musick Can Haz Scope? Can Haz Scope? http://www.flickr.com/photos/35445050@N00/6218860576/
2. What scope? • I'm not talking about variable scope. • $ ri scope
3. What can be scoped? Routes, Models Models, Rake Tasks Implementation from Description ActionDispatch ::Routing::Mapper::Scoping scope(*args) { || ... } Scopes a set of routes to the given default options. ActiveRecord ::Associations::CollectionProxy Scope() Returns a Relation object for the records in this association ActiveRecord ::DeprecatedFinders scope(name, body = {}, &block) ActiveRecord ::Reflection::MacroReflection#sco pe ActiveRecord ::Scoping::Named::ClassMethods scope(name, body, &block) Rake::Task#scope Array of nested namespaces names used for task lookup by this task.
4. Scoping Models, Part 1 From ActiveRecord::Scoping::Named::ClassMethods “scope” adds a class method for retrieving and querying objects: it's a way to narrow a database query. def scope(name, body, &block) extension = Module.new(&block) if block singleton_class.send(:define_method, name) do |*args| scope = all.scoping { body.call(*args) } scope = scope.extending(extension) if extension scope || all end end
5. Scoping Models, Part 2 • Scopes are simply 'syntactic sugar' for defining a class method. This: Same as: SQL: scope :tabby, -> { where(coat_coloration: 'tabby') } def self.tabby where(coat_coloration: 'tabby') end SELECT “cats”.* FROM “cats” WHERE “cats”.”coat_coloration” = “tabby”;
6. Taking advantage Cat.tabby.first Cat.tabby.kitten Cat.tabby.count Cat.kitten.tabby.count Cat.tabby.each(&block) The object returned by calling a scope on its class resembles the object constructed by a has_many declaration. These methods are also available to has_many associations. cat_palace.cats.tabby.first cat_palace.cats.tabby.kitten cat_palace.cats.tabby.count cat_palace.cats.kitten.tabby.count cat_palace.cats.tabby.each(&block)
7. gem 'has_scope' Maps controller filters to resource scopes # Define scope in model # Use as filters by declaring has_scope in controller and apply scopes to a resource by calling apply_scopes # Send request for LOLcats class Cat < ActiveRecord::Base scope :LOL, -> { where(funny: true) } end class CatsController < ApplicationController has_scope :LOL, type: :boolean def index @cats = apply_scopes(Cat).all end end /cats?LOL=true
8. Yes, model cat Yes, model cat can haz scope. can haz scope. http://www.flickr.com/photos/35445050@N00/6218860576/
9. Resources • $ ri scope • http://api.rubyonrails.org/classes/ActiveRecord/Scopi ng/Named/ClassMethods.html#method-i-scope • https://github.com/rails/rails/blob/master/activerecord /lib/active_record/scoping/named.rb • http://guides.rubyonrails.org/active_record_querying. html#scopes • https://github.com/plataformatec/has_scope