Rails recursive association with migrations

Question

I have a table named Nodes. Each node belongs to one father of the same table, and has one child on the same table too. This is the Node model:

class Node < ApplicationRecord
    belongs_to :parent # I tried using :node instead of :parent
    has_one :children # Same than above
end

How can I easily achieve this?

Answer 1

I belive what you are looking for is something like this:

class CreateNodes < ActiveRecord::Migration[5.0]
  def change
    create_table :nodes do |t|
      t.belongs_to :parent, 
        foreign_key: { to_table: :nodes },
        null: true

      t.timestamps
    end
  end
end

---

class Node < ApplicationRecord
  belongs_to :parent, class_name: 'Node', optional: true
  has_many :children, class_name: 'Node', foreign_key: 'parent_id'
end

It sets up a self-referential 1-to-many association between a node and its children.

Answer 2

Self-Referential Association

class Node < ApplicationRecord
    belongs_to :parent , :class_name => "Node", :foreign_key => "parent_id", optional: true
    has_one :child, :class_name => "Node", :foreign_key => "parent_id" 
end

In that case you should have parent_id in Node model. Also for has_one relationship it should be child not children by convention.

Query will be like this: -

parent = Node.create(parent_id: nil)
child = Node.create(parent_id: parent.id)

Get all parent =>

Node.where(parent_id: nil)

Get child of a parent =>

parent.child