Why You Might Not Use Named Scopes In Rails3

It’s interesting how Rails 3 querying is a lot easier than it was before.

Simple Task: Get all posts that are promoted to front page.

Some apps probably do not use the field “promoted” primarily because there’s a published field then all published posts will be promoted on front page. But in Drupal, nodes have promoted field and I think most apps should too. Sometimes you wouldn’t want to show everything on the front page or want some post on top of the list of posts.

Write the tests first.

spec/fixtures/post.yml

hello_world:
  title: Hello World
  body: "We are ruby enthusiasts"
  promoted: true


spec/models/post_spec.rb

require 'spec_helper'

describe Post do
  before(:each) do
    @post = Post.new
    @date = Time.now
  end

 
  describe 'return promoted post' do
    it 'gets promoted posts' do
      Post.promoted.size.should == 1
    end
  end 

end

The test could be written in a better way. But this is just written to make sure there are returns for that method. Run “rake spec”. It should show an error.

app/models/post.rb


BEFORE:

named_scope :promoted, :conditions => { :promoted => true }

(In Rails 3, named_scope is now scope)

AFTER: 

def self.promoted
  where(:promoted => true)
end

That is it for the models. Rails 3 is much better, really.

BEFORE:

app/controllers/posts_controller.rb

Post.find(:all, :conditions=>{:promoted => true}, :order=>"created_at DESC")

or modify the named scope:


app/models/post.rb

named_scope :promoted, :conditions => { :promoted => true }, :order=>"created_at DESC"


AFTER: 

app/models/post.rb


Post.promoted.order("created_at DESC")

With the new querying API, we don’t have to assume the order is always “created_at DESC”. It’s quite flexible and concise. Just as DHH mentioned in the RailsConf 2010, one of the strengths of Rails 3 is to build queries on stages.