ruby-on-rails - rails : Many to many relation to self

Question

我在创建此关联时遇到问题:考虑模型“Entry”。我希望条目有很多条目作为 parent ，我希望条目有很多条目作为 child 。我想通过一个我称之为“关联”的模型来实现这种关系，所以这是我尝试过的:

迁移:

class CreateAssociations < ActiveRecord::Migration[5.0]
  def change
    create_table :associations do |t|
      t.integer :parent_id
      t.integer :child_id
    end
  end
end

关联模型:

class Association < ApplicationRecord
  belongs_to :parent, class_name: 'Entry'
  belongs_to :child, class_name: 'Entry'
end

到目前为止它有效。但是现在我如何使用它来创建模型到自身的两个多对多关系？

class Entry < ApplicationRecord
  # has many parent entries of type entry via table associations and child_id
  # has many child entries of type entry via table associations and parent_id
end

Answer 1

这应该有效:

class Entry < ApplicationRecord
  has_and_belongs_to_many :parents, class_name: 'Entry', join_table: :associations, foreign_key: :child_id, association_foreign_key: :parent_id
  has_and_belongs_to_many :children, class_name: 'Entry', join_table: :associations, foreign_key: :parent_id, association_foreign_key: :child_id
end