Question

I am building an application where a User can have many Clients (which cannot be shared among Users).

It is a fairly small application but it could happen that two Clients belong to the same Organisation. So it would be nice to have an extra table to hold all the information about the Organisation. It could also happen that a Client is a private Client and does not belong to any Organisation.

I know in database design this is fairly common, but how can this be modelled in Rails?

Answer 1

The answer is what have been stated by @peter-duijnstee, with the additional constraints asked:

class Organization < ActiveRecord::Base
  belongs_to :user
  validates :user, :presence => true
end

class Client < ActiveRecord::Base
  belongs_to :user
  belongs_to :organization

  # note the final "s", it validates a field
  validates :user, :presence => true 

  # no final "s", validate using a method
  validate :organization_user, :if => :organization_present?

  def organization_present?
    organization.present?
  end

  def organization_user
    errors.add(:organization_id, "is not allowed") unless organization.user_id == user_id
  end
end