ranked-model is a modern row sorting library built for Rails 3 & 4. It uses ARel aggressively and is better optimized than most other libraries.

ranked-model passes specs with Rails 3.1, 3.2, 4.0, and 4.1-beta for MySQL, Postgres, and SQLite on Ruby 1.9.2, 1.9.3, 2.0, 2.1, jruby-19mode, and rubinius where Rails supports the platform. This is with the exception of Postgres before Rails 4.0 on all platforms, which is unsupported (I'd gladly accept a PR to fix this).

TL;DR, if you are using Rails 4 and up you are 100% good to go. Before Rails 4, be wary of Postgres.

To install ranked-model, just add it to your Gemfile:

gem 'ranked-model'

# Or pin ranked-model to git
# gem 'ranked-model',
#   :git => 'git@github.com:mixonic/ranked-model.git'

Then use bundle install to update your Gemfile.lock.

Use of ranked-model is straight ahead. Get some ducks:

class Duck < ActiveRecord::Base
end

Put your ducks in a row:

class Duck < ActiveRecord::Base

  include RankedModel
  ranks :row_order

end

This simple example assumes an integer column called row_order. To order Ducks by this order:

Duck.rank(:row_order).all

The ranking integers stored in the row_order column will be big and spaced apart. When you implement a sorting UI, just update the resource by appending the column name with _position and indicating the desired position:

@duck.update_attribute :row_order_position, 0  # or 1, 2, 37. :first, :last, :up and :down are also valid

Position numbers begin at zero. A position number greater than the number of records acts the same as :last. :up and :down move the record up/down the ladder by one step.

So using a normal json controller where @duck.attributes = params[:duck]; @duck.save, JS can look pretty elegant:

$.ajax({
  type: 'PUT',
  url: '/ducks',
  dataType: 'json',
  data: { duck: { row_order_position: 0 } },  // or whatever your new position is
});

The ranks method takes serveral arguments:

class Duck < ActiveRecord::Base

  include RankedModel

  ranks :row_order,           # Name this ranker, used with rank()
    :column => :sort_order    # Override the default column, which defaults to the name
  
  belongs_to :pond
  ranks :swimming_order,
    :with_same => :pond_id    # Ducks belong_to Ponds, make the ranker scoped to one pond
  
  scope :walking, where(:walking => true )
  ranks :walking_order,
    :scope => :walking        # Narrow this ranker to a scope

end

When you make a query, add the rank:

Duck.rank(:row_order)

Pond.first.ducks.rank(:swimming_order)

Duck.walking.rank(:walking)

ranked-model scopes your records' positions based on the class name of the object. If you have a STI type column set in your model, ranked-model will reference that class for positioning.

Consider this example:

class Vehicle < ActiveRecord::Base
  ranks :row_order
end

class Car < Vehicle
end

class Truck < Vehicle
end

car = Car.create!
truck = Truck.create!

car.row_order
=> 0
truck.row_order
=> 0

In this example, the row_order for both car and truck will be set to 0 because they have different class names (Car and Truck, respectively).

If you would like for both car and truck to be ranked together based on the base Vehicle class instead, use the class_name option:

class Vehicle < ActiveRecord::Base
  ranks :row_order, class_name: 'Vehicle'
end

class Car < Vehicle
end

class Truck < Vehicle
end

car = Car.create!
truck = Truck.create!

car.row_order
=> 0
truck.row_order
=> 4194304

This library is written using ARel from the ground-up. This leaves the code much cleaner than many implementations. ranked-model is also optimized to write to the database as little as possible: ranks are stored as a number between -8388607 and 8388607 (the MEDIUMINT range in MySQL). When an item is given a new position, it assigns itself a rank number between two neighbors. This allows several movements of items before no digits are available between two neighbors. When this occurs, ranked-model will try to shift other records out of the way. If items can't be easily shifted anymore, it will rebalance the distribution of rank numbers across all members of the ranked group.

Fork, clone, write a test, write some code, commit, push, send a pull request. Github FTW!

The specs can be run with sqlite, postgres, and mysql:

DB=postgres bundle exec rake

Is no DB is specified, the tests run against sqlite.

RankedModel is mostly the handiwork of Matthew Beale:

• madhatted.com is where I blog. Also @mixonic.

A hearty thanks to these contributors:

• Harvest where this Gem started. They are great, great folks.
• yabawock
• AndrewRadev
• adheerajkumar
• mikeycgto
• robotex82
• rociiu
• codepodu
• kakra
• metalon
• jamesalmond
• jguyon
• pehrlich
• petergoldstein