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https://github.com/brendon/ranked-model

An acts_as_sortable/acts_as_list replacement built for Rails 4+
https://github.com/brendon/ranked-model

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An acts_as_sortable/acts_as_list replacement built for Rails 4+

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README 

        
**ranked-model** is a modern row sorting library built for Rails 4.2+.  It uses ARel aggressively and is better optimized than most other libraries.



[![Build Status](https://github.com/brendon/ranked-model/actions/workflows/ci.yml/badge.svg)](https://github.com/brendon/ranked-model/actions/workflows/ci.yml)



ANNOUNCING: Positioning, the gem

--------------------------------



As maintainer of both Acts As List and the Ranked Model gems, I've become intimately aquainted with the strengths and weaknesses of each. I ended up writing a small scale Rails Concern for positioning database rows for a recent project and it worked really well so I've decided to release it as a gem: [Positioning](https://github.com/brendon/positioning)



Positioning works similarly to Acts As List in that it maintains a sequential list of integer values as positions. It differs in that it encourages a unique constraints on the position column and supports multiple lists per database table. It borrows Ranked Model's concept of relative positioning. I encourage you to check it out and give it a whirl on your project!



Installation

------------



ranked-model passes specs with Rails 4.2, 5.0, 5.1, 5.2, 6.0 and 6.1 for MySQL, Postgres, and SQLite on Ruby 2.4 through 3.0 (with exceptions, please check the CI setup for supported combinations), and jruby-9.1.17.0 where Rails supports the platform.



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



``` ruby

gem 'ranked-model'



# Or pin ranked-model to git

# gem 'ranked-model',

#   git: '[email protected]: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:



``` ruby

class Duck < ActiveRecord::Base

end

```



Give them an order (integer column):



```bash

rails g migration AddRowOrderToDucks row_order:integer

rails db:migrate

```



**IMPORTANT: The `_order` table column MUST allow null values. For the reason behind this requirement see [issue#167](https://github.com/mixonic/ranked-model/issues/167)**



Put your ducks in a row:



``` ruby

class Duck < ActiveRecord::Base



  include RankedModel

  ranks :row_order



end

```



Order the Ducks by this order:



``` ruby

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:



``` ruby

@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:



``` javascript

$.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.



``` ruby

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:



``` ruby

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



  belongs_to :parent, class_name: 'Duck', optional: true

  ranks :child_order,

    unless: :has_no_parent?,         # Rank only ducks that have a parent. Alternatively a Proc or lambda can be passed, e.g. proc { parent.nil? }

    with_same: :parent_id



  def has_no_parent?

    parent.nil?

  end

end

```



When you make a query, add the rank:



``` ruby

Duck.rank(:row_order)



Pond.first.ducks.rank(:swimming_order)



Duck.walking.rank(:walking)

```



Drawbacks

---------



While ranked-model is performant when storing data, it might cause N+1s depending on how you write your code. Consider this snippet:



```ruby

ducks = Duck.all

ducks.map do |duck|

  {

    id: duck.id,

    position: duck.row_order_rank # This causes N+1!

  }

end

```



Every call to `duck.row_order_rank` will make a call to the DB to check the rank of that

particular element. If you have a long list of elements this might cause issues to your DB.



In order to avoid that, you can use the `rank(:your_rank)` scope and some Ruby code to get

the element's position:



```ruby

ducks = Duck.rank(:row_order).all

ducks.map.with_index do |duck, index|

  {

    id: duck.id,

    position: index

  }

end

```



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:



``` ruby

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:



``` ruby

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

```



Migrations for existing data

----------------------------



If you use `ranked_model` with existing data, the following migration (for Rails

6) can be a starting point. Make sure to declare `include RankedModel` and

`ranks :row_order` in your `Duck` before running the migration.



```bash

rails g migration AddRowOrderToDucks row_order:integer

```



Then, adjust the migration:

```ruby

# e.g. file db/migrate/20200325095038_add_row_order_to_ducks.rb

class AddRowOrderToDucks < ActiveRecord::Migration[6.0]

  def change

    add_column :ducks, :row_order, :integer



    # Newest Duck shall rank "highest"" (be last).

    Duck.update_all('row_order = EXTRACT(EPOCH FROM created_at)')



    # Alternatively, implement any other sorting default

    # Duck.order(created_at: :desc).each do |duck|

    #   duck.update!(row_order: duck.created_at.to_i + duck.age / 2)

    # end

  end

end

```



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.



Record updates to rebalance ranks do not trigger ActiveRecord callbacks. If you need to react to these updates

(to index them in a secondary data store, for example), you can subscribe to the `ranked_model.ranks_updated`

[ActiveSupport notification](https://api.rubyonrails.org/v7.1/classes/ActiveSupport/Notifications.html).

Subscribed consumers receive an event for each rearrangement or rebalancing, the payload of which includes the

triggering instance and the `scope` and `with_same` options for the ranking, which can be used to retrieve the

affected records.



```ruby

ActiveSupport::Notifications.subscribe("ranked_model.ranks_updated") do |_name, _start, _finish, _id, payload|

  # payload[:instance] - the instance whose update triggered the rebalance

  # payload[:scope] - the scope applied to the ranking

  # payload[:with_same] - the with_same option applied to the ranking

end

```



Contributing

------------



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



The code is published under the [MIT License](LICENSE).



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](http://madhatted.com) is where I blog. Also [@mixonic](http://twitter.com/mixonic).



A hearty thanks to these contributors:



* [Harvest](http://getharvest.com) where this Gem started. They are great, great folks.

* [yabawock](https://github.com/yabawock)

* [AndrewRadev](https://github.com/AndrewRadev)

* [adheerajkumar](https://github.com/adheerajkumar)

* [mikeycgto](https://github.com/mikeycgto)

* [robotex82](https://github.com/robotex82)

* [rociiu](https://github.com/rociiu)

* [codepodu](https://github.com/codepodu)

* [kakra](https://github.com/kakra)

* [metalon](https://github.com/metalon)

* [jamesalmond](https://github.com/jamesalmond)

* [jguyon](https://github.com/jguyon)

* [pehrlich](https://github.com/pehrlich)

* [petergoldstein](https://github.com/petergoldstein)

* [brendon](https://github.com/brendon)