ranked-model

ranked-model is a modern row sorting library built for Rails 3, 4 and 5. It uses ARel aggressively and is better optimized than most other libraries.

Installation

ranked-model passes specs with Rails 4.2, 5.0, 5.1, 5.2, 6.0 for MySQL, Postgres, and SQLite on Ruby 2.4 through 2.6, and jruby-9.1.17.0 where Rails supports the platform. This is with the exception of Postgres before Rails 4.0 on all platforms, which is unsupported by ranked-model. Note that the pg gem has pulled support for rbx (Rubinius) from version 1 onward.

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.

Simple Use

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 :row_order_position => 0  # or 1, 2, 37. :first, :last, :up and :down are also valid

IMPORTANT: Note that you MUST append _position to the column name when setting a new position on an instance. This is a fake column that can take relative as well as absolute index-based values for position.

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
});

If you need to find the rank of an item with respect to other ranked items, you can use the {column_name}_rank method on the model instance. {column_name} is your resource ranking column.

Following on from our examples above, the row_order_rank method will return the position of the duck object in the list with respect to the order defined by the row_order column.

Duck.rank(:row_order).first.row_order_rank # => 0
Duck.rank(:row_order).third.row_order_rank # => 2

Complex Use

The ranks method takes several 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

  ranks :row_order,
    :with_same => [:pond_id, :breed] # Lets rank them by breed

  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)

Single Table Inheritance (STI)

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

Internals

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 -2147483648 and 2147483647 (the INT 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.

Contributing

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:

bundle
appraisal install
DB=postgresql bundle exec appraisal rake

If no DB is specified (sqlite, mysql, or postgresql), 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
• brendon