**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: '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:

``` 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)
