多级分类gem: awesome_nested_set

https://github.com/collectiveidea/awesome_nested_set

修改Gemfile

gem 'awesome_nested_set'

1， 生成对应的文件

rails g scaffold category name:string parent_id:integer lft:integer rgt:integer depth:integer 

2， 修改model

class Category < ActiveRecord::Base
  acts_as_nested_set
  attr_accessible :name, :parent_id
end

3, 修改views

<%= 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}" } ) %>

4, 如何取得指定category的所有的children和nest children

category.descendants  

        # Returns a set of itself and all of its nested children
        def self_and_descendants
          nested_set_scope.where([
            "#{self.class.quoted_table_name}.#{quoted_left_column_name} >= ? AND #{self.class.quoted_table_name}.#{quoted_left_column_name} < ?", left, right
            # using _left_ for both sides here lets us benefit from an index on that column if one exists
          ])
        end

        # Returns a set of all of its children and nested children
        def descendants
          without_self self_and_descendants
        end