# Awesome Nested Set
[](https://github.com/collectiveidea/awesome_nested_set/actions/workflows/ci.yml) [](https://codeclimate.com/github/collectiveidea/awesome_nested_set) [](https://hakiri.io/github/collectiveidea/awesome_nested_set/master)
Awesome Nested Set is an implementation of the nested set pattern for ActiveRecord models.
It is a replacement for acts_as_nested_set and BetterNestedSet, but more awesome.
Version 3.2 supports Rails 6, 3.1 supports Rails 5 & 4. Version 2 supports Rails 3.
Gem versions prior to 2.0 support Rails 2.
## What makes this so awesome?
This is a new implementation of nested set based off of BetterNestedSet that fixes some bugs, removes tons of duplication, adds a few useful methods, and adds STI support.
## Installation
Add to your Gemfile:
```ruby
gem 'awesome_nested_set'
```
## Usage
To make use of `awesome_nested_set` your model needs to have 3 fields:
`lft`, `rgt`, and `parent_id`. The names of these fields are configurable.
You can also have optional fields: `depth` and `children_count`. These fields are configurable.
Note that the `children_count` column must have `null: false` and `default: 0` to
function properly.
```ruby
class CreateCategories < ActiveRecord::Migration
def change
create_table :categories do |t|
t.string :name
t.integer :parent_id, null: true, index: true
t.integer :lft, null: false, index: true
t.integer :rgt, null: false, index: true
# optional fields
t.integer :depth, null: false, default: 0
t.integer :children_count, null: false, default: 0
t.timestamps
end
end
end
```
Enable the nested set functionality by declaring `acts_as_nested_set` on your model
```ruby
class Category < ActiveRecord::Base
acts_as_nested_set
end
```
Run `rake rdoc` to generate the API docs and see [CollectiveIdea::Acts::NestedSet](lib/awesome_nested_set/awesome_nested_set.rb) for more information.
## Options
You can pass various options to `acts_as_nested_set` macro. Configuration options are:
* `parent_column`: specifies the column name to use for keeping the position integer (default: parent_id)
* `primary_column`: specifies the column name to use as the inverse of the parent column (default: id)
* `left_column`: column name for left boundary data (default: lft)
* `right_column`: column name for right boundary data (default: rgt)
* `depth_column`: column name for the depth data default (default: depth)
* `scope`: restricts what is to be considered a list. Given a symbol, it'll attach `_id` (if it hasn't been already) and use that as the foreign key restriction. You can also pass an array to scope by multiple attributes. Example: `acts_as_nested_set :scope => [:notable_id, :notable_type]`
* `dependent`: behavior for cascading destroy. If set to :destroy, all the child objects are destroyed alongside this object by calling their destroy method. If set to :delete_all (default), all the child objects are deleted without calling their destroy method. If set to :nullify, all child objects will become orphaned and become roots themselves.
* `counter_cache`: adds a counter cache for the number of children. defaults to false. Example: `acts_as_nested_set :counter_cache => :children_count`
* `order_column`: on which column to do sorting, by default it is the left_column_name. Example: `acts_as_nested_set :order_column => :position`
* `touch`: If set to `true`, then the updated_at timestamp on the ancestors will be set to the current time whenever this object is saved or destroyed (default: false)
See [CollectiveIdea::Acts::NestedSet::Model::ClassMethods](/lib/awesome_nested_set/model.rb#L26) for a list of class methods and [CollectiveIdea::Acts::NestedSet::Model](lib/awesome_nested_set/model.rb#L13) for a list of instance methods added to acts_as_nested_set models
## Indexes
It is highly recommended that you add an index to the `rgt` column on your models. Every insertion requires finding the next `rgt` value to use and this can be slow for large tables without an index. It is probably best to index the other fields as well (`parent_id`, `lft`, `depth`).
## Callbacks
There are three callbacks called when moving a node:
`before_move`, `after_move` and `around_move`.
```ruby
class Category < ActiveRecord::Base
acts_as_nested_set
after_move :rebuild_slug
around_move :da_fancy_things_around
private
def rebuild_slug
# do whatever
end
def da_fancy_things_around
# do something...
yield # actually moves
# do something else...
end
end
```
Beside this there are also hooks to act on the newly added or removed children.
```ruby
class Category < ActiveRecord::Base
acts_as_nested_set :before_add => :do_before_add_stuff,
:after_add => :do_after_add_stuff,
:before_remove => :do_before_remove_stuff,
:after_remove => :do_after_remove_stuff
private
def do_before_add_stuff(child_node)
# do whatever with the child
end
def do_after_add_stuff(child_node)
# do whatever with the child
end
def do_before_remove_stuff(child_node)
# do whatever with the child
end
def do_after_remove_stuff(child_node)
# do whatever with the child
end
end
```
## Protecting attributes from mass assignment (for Rails < 4)
It's generally best to "whitelist" the attributes that can be used in mass assignment:
```ruby
class Category < ActiveRecord::Base
acts_as_nested_set
attr_accessible :name, :parent_id
end
```
If for some reason that is not possible, you will probably want to protect the `lft` and `rgt` attributes:
```ruby
class Category < ActiveRecord::Base
acts_as_nested_set
attr_protected :lft, :rgt
end
```
## Add to your existing project
To make use of `awesome_nested_set`, your model needs to have 3 fields:
`lft`, `rgt`, and `parent_id`. The names of these fields are configurable.
You can also have optional fields, `depth` and `children_count`.
Create a migration to add fields:
```ruby
class AddNestedToCategories < ActiveRecord::Migration
def self.up
add_column :categories, :parent_id, :integer # Comment this line if your project already has this column
# Category.where(parent_id: 0).update_all(parent_id: nil) # Uncomment this line if your project already has :parent_id
add_column :categories, :lft, :integer
add_column :categories, :rgt, :integer
# optional fields
add_column :categories, :depth, :integer
add_column :categories, :children_count, :integer
# This is necessary to update :lft and :rgt columns
Category.reset_column_information
Category.rebuild!
end
def self.down
remove_column :categories, :parent_id
remove_column :categories, :lft
remove_column :categories, :rgt
# optional fields
remove_column :categories, :depth
remove_column :categories, :children_count
end
end
```
Enable the nested set functionality by declaring `acts_as_nested_set` on your model
```ruby
class Category < ActiveRecord::Base
acts_as_nested_set
end
```
Your project is now ready to run with the `awesome_nested_set` gem!
## Conversion from other trees
Coming from acts_as_tree or another system where you only have a parent_id? No problem. Simply add the lft & rgt fields as above, and then run:
```ruby
Category.rebuild!
```
Your tree will be converted to a valid nested set. Awesome!
Note: You can use `Category.rebuild!(false)` to skip model validations when performing the rebuild.
## View Helper
The view helper is called #nested_set_options.
Example usage:
```erb
<%= f.select :parent_id, nested_set_options(Category, @category) {|i| "#{'-' * i.level} #{i.name}" } %>
<%= select_tag 'parent_id', options_for_select(nested_set_options(Category) {|i| "#{'-' * i.level} #{i.name}" } ) %>
```
See [CollectiveIdea::Acts::NestedSet::Helper](lib/awesome_nested_set/helper.rb) for more information about the helpers.
## How to contribute
Please see the ['Contributing' document](CONTRIBUTING.md).
Copyright © 2008–2015 [Collective Idea](http://collectiveidea.com), released under the MIT license.