要进行实际的自引用关联，只需在users表中添加一列，该列指向同一个表：

class AddGodfatherToUsers < ActiveRecord::Migration[6.1]                                                                                                                                       
  def change                                                                                                                                                                                      
    add_reference :users, :godfather, null: true, 
                                      foreign_key: { to_table: :users }                                                                                                                           
  end                                                                                                                                                                                        end

class User
  belongs_to :god_father,
    class_name: 'User',
    optional: true,
    inverse_of: :god_children
  has_many :god_children,
    class_name: 'User',
    foreign_key: :god_father_id
    inverse_of: :god_father
end

如果你必须将Referalls存储为一个单独的表，你的思路是对的，但是你把外键弄反了：

class Referral < ApplicationRecord
  # you better be explicit here or its going to get extremely confusing
  belongs_to :godfather, class_name: 'User' 
  belongs_to :godson, class_name: 'User'
end

class User < ApplicationRecord
  has_many :referrals_as_godfather, 
    class_name: 'Referral', foreign_key: 'godfather_id'
  has_one :referral_as_godson, 
    class_name: 'Referral', 
    foreign_key: 'godfather_id'
  has_many :godsons, through: :referrals_as_godfather
  has_one :godfather, through: :referral_as_godson
end

需要注意的是，has_one并不保证一个用户只能有一个推荐（因此只有一个教父），它只是给查询添加了一个LIMIT 1，您必须通过唯一性约束和验证来强制执行。