ActsAsList

Description

This acts_as extension provides the capabilities for sorting and reordering a number of objects in a list. The class that has this specified needs to have a position column defined as an integer on the mapped database table.

0.8.0 Upgrade Notes

There are a couple of changes of behaviour from 0.8.0 onwards:

If you specify add_new_at: :top, new items will be added to the top of the list like always. But now, if you specify a position at insert time: .create(position: 3), the position will be respected. In this example, the item will end up at position 3 and will move other items further down the list. Before 0.8.0 the position would be ignored and the item would still be added to the top of the list. #220
acts_as_list now copes with disparate position integers (i.e. gaps between the numbers). There has been a change in behaviour for the higher_items method. It now returns items with the first item in the collection being the closest item to the reference item, and the last item in the collection being the furthest from the reference item (a.k.a. the first item in the list). #223

Installation

In your Gemfile:

gem 'acts_as_list'

Or, from the command line:

gem install acts_as_list

Example

At first, you need to add a position column to desired table:

rails g migration AddPositionToTodoItem position:integer
rake db:migrate

After that you can use acts_as_list method in the model:

class TodoList < ActiveRecord::Base
  has_many :todo_items, -> { order(position: :asc) }
end

class TodoItem < ActiveRecord::Base
  belongs_to :todo_list
  acts_as_list scope: :todo_list
end

todo_list = TodoList.find(...)
todo_list.todo_items.first.move_to_bottom
todo_list.todo_items.last.move_higher

Instance Methods Added To ActiveRecord Models

You'll have a number of methods added to each instance of the ActiveRecord model that to which acts_as_list is added.

In acts_as_list, "higher" means further up the list (a lower position), and "lower" means further down the list (a higher position). That can be confusing, so it might make sense to add tests that validate that you're using the right method given your context.

Methods That Change Position and Reorder List

list_item.insert_at(2)
list_item.move_lower will do nothing if the item is the lowest item
list_item.move_higher will do nothing if the item is the highest item
list_item.move_to_bottom
list_item.move_to_top
list_item.remove_from_list

Methods That Change Position Without Reordering List

list_item.increment_position
list_item.decrement_position
list_item.set_list_position(3)

Methods That Return Attributes of the Item's List Position

list_item.first?
list_item.last?
list_item.in_list?
list_item.not_in_list?
list_item.default_position?
list_item.higher_item
list_item.higher_items will return all the items above list_item in the list (ordered by the position, ascending)
list_item.lower_item
list_item.lower_items will return all the items below list_item in the list (ordered by the position, ascending)

Adding `acts_as_list` To An Existing Model

As it stands acts_as_list requires position values to be set on the model before the instance methods above will work. Adding something like the below to your migration will set the default position. Change the parameters to order if you want a different initial ordering.

class AddPositionToTodoItem < ActiveRecord::Migration
  def change
    add_column :todo_items, :position, :integer
    TodoItem.order(:updated_at).each.with_index(1) do |todo_item, index|
      todo_item.update_column :position, index
    end
  end
end

If you are using the scope option things can get a bit more complicated. Let's say you have acts_as_list scope: :todo_list, you might instead need something like this:

TodoList.all.each do |todo_list|
  todo_list.todo_items.order(:updated_at).each.with_index(1) do |todo_item, index|
    todo_item.update_column :position, index
  end
end

Notes

All position queries (select, update, etc.) inside gem methods are executed without the default scope (i.e. Model.unscoped), this will prevent nasty issues when the default scope is different from acts_as_list scope.

The position column is set after validations are called, so you should not put a presence validation on the position column.

If you need a scope by a non-association field you should pass an array, containing field name, to a scope:

class TodoItem < ActiveRecord::Base
  # `kind` is a plain text field (e.g. 'work', 'shopping', 'meeting'), not an association
  acts_as_list scope: [:kind]
end

More Options

column default: position. Use this option if the column name in your database is different from position.
top_of_list default: 1. Use this option to define the top of the list. Use 0 to make the collection act more like an array in its indexing.
add_new_at default: :bottom. Use this option to specify whether objects get added to the :top or :bottom of the list. nil will result in new items not being added to the list on create, i.e, position will be kept nil after create.

Disabling temporarily

If you need to temporarily disable acts_as_list during specific operations such as mass-update or imports:

TodoItem.acts_as_list_no_update do
  perform_mass_update
end

In an acts_as_list_no_update block, all callbacks are disabled, and positions are not updated. New records will be created with the default value from the database. It is your responsibility to correctly manage positions values.

You can also pass an array of classes as an argument to disable database updates on just those classes. It can be any ActiveRecord class that has acts_as_list enabled.

class TodoList < ActiveRecord::Base
  has_many :todo_items, -> { order(position: :asc) }
  acts_as_list
end

class TodoItem < ActiveRecord::Base
  belongs_to :todo_list
  has_many :todo_attachments, -> { order(position: :asc) }

  acts_as_list scope: :todo_list
end

class TodoAttachment < ActiveRecord::Base
  belongs_to :todo_list
  acts_as_list scope: :todo_item
end

TodoItem.acts_as_list_no_update([TodoAttachment]) do
  TodoItem.find(10).update(position: 2)
  TodoAttachment.find(10).update(position: 1)
  TodoAttachment.find(11).update(position: 2)
  TodoList.find(2).update(position: 3) # For this instance the callbacks will be called because we haven't passed the class as an argument
end

Versions

Version 0.9.0 adds acts_as_list_no_update (https://github.com/swanandp/acts_as_list/pull/244) and compatibility with not-null and uniqueness constraints on the database (https://github.com/swanandp/acts_as_list/pull/246). These additions shouldn't break compatibility with existing implementations.

As of version 0.7.5 Rails 5 is supported.

All versions 0.1.5 onwards require Rails 3.0.x and higher.

Build Status

Workflow Status

Roadmap

Sort based feature

Contributing to `acts_as_list`

Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet
Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it
Fork the project
Start a feature/bugfix branch
Commit and push until you are happy with your contribution
Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.
I would recommend using Rails 3.1.x and higher for testing the build before a pull request. The current test harness does not quite work with 3.0.x. The plugin itself works, but the issue lies with testing infrastructure.