Creating has_many association with ancestry gem

问题

I installed ancestry gem & create Location Structure.

• Alaska
• California
  • Los Angeles
  • Fresno
  • Cincotta (Fresno)
  • Hammond (Fresno)
    • Melvin (Fresno)
      • Melvin 1
      • Melvin 2
      • Melvin 3
• Arizona
• Colorado

My post and location model

class Location < ActiveRecord::Base
 include Tree
 has_many :posts
end

class Post < ActiveRecord::Base
  belongs_to :location
end

When i am add new post, how to display only depth 4 level ( Melvin 1,Melvin 2,Melvin 3) as drop down.

回答1:

You have to enable cache depth so you can use at_depth:

Location.all.at_depth(4)

Thiscan be used to render a select input element:

<%= select :location_id, Location.all.at_depth(4) { |l| [ l.name, l.id ] } %>

来源：https://stackoverflow.com/questions/24787750/creating-has-many-association-with-ancestry-gem