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# AwesomeNestedSet
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 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.
[](https://codeclimate.com/github/collectiveidea/awesome_nested_set)
## 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 an optional field, `depth`:
```ruby
class CreateCategories < ActiveRecord::Migration
def self.up
create_table :categories do |t|
t.string :name
t.integer :parent_id
t.integer :lft
t.integer :rgt
t.integer :depth # this is optional.
end
end
def self.down
drop_table :categories
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.
## 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
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
```
## 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!
## 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.
## References
You can learn more about nested sets at: http://threebit.net/tutorials/nestedset/tutorial1.html
## How to contribute
Please see the ['Contributing' document](CONTRIBUTING.md).
Copyright © 2008 - 2013 Collective Idea, released under the MIT license
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