awesome_nested_set: import git 2-1-stable branch revision 606847769 (#6579)

https://github.com/collectiveidea/awesome_nested_set/commit/606847769

git-svn-id: http://svn.redmine.org/redmine/trunk@13143 e93f8b46-1217-0410-a6f0-8f06a7374b81

lib/plugins/awesome_nested_set/README.md

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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.
+
+[![Code Climate](https://codeclimate.com/github/collectiveidea/awesome_nested_set.png)](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