Manager -> Employee association one level in rails

I want to create manager->employee association.

• Manager have many employees
• Employee belongs to only one manager
• Manager does not have another manager

How to implement this design ? I created something closer(code is below) but in my design manager can have other manager.

class User < ApplicationRecord
  has_many :employee, class_name: "User", foreign_key: "manager_id"
  belongs_to :manager, class_name: "User", foreign_key: "manager_id"
end

Any help is highly appreciated!

What you have is a really standard self-joining setup (with a few small issues). You can limit the depth of the tree by just adding a custom validation:

class User < ApplicationRecord
  # optional: true is needed in Rails 5+ since belongs_to is no
  # longer optional by default
  belongs_to :manager, class_name: 'User',
                       optional: true
  # pay attention to pluralization
  has_many :employees, class_name: 'User',
                       foreign_key: 'manager_id'
  # calls the custom validation we will define later
  validate :manager_must_be_a_manager, unless: :manager?

  def manager?
    manager.nil?
  end

  private
    # our custom validation method
    def manager_must_be_a_manager
      errors.add(:manager, 'is not a manager') unless manager.manager?
    end
end

So now if we run:

user_1 = User.create!
user_2 = User.create!(manager: user_1)
User.create!(manager: user_2)

The third line will raise ActiveRecord::RecordInvalid: Validation failed: Manager is not a manager.