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

Installation

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

gem 'ranked-model'

# Or pin ranked-model to git
# gem 'ranked-model',
#   :git => '[email protected]:harvesthq/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 with the position instead:

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

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
});

Complex Use

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)

Internals

This libarary 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 memebers of the ranked group.

Contributing

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

This project was open-sourced by Harvest. We're hiring!

A hearty thanks to these contributors: