Question

In my application a user can create an appointment.

class User
    has_many :appointments
end

class Appointment
    belongs_to :user
end

However, a user can also join another appointment created by another user.

Could someone recommend a way to set up my models?

I’ve been reading through http://guides.rubyonrails.org/association_basics.html and cannot find the correct association.

I’m really keen to do this the rails way, rather than hacking my application about.

Would has_and_belongs_to_many be the way to go?

Answer 1

Sounds like you probably want to use has_many with some kind of model describing the relationship between users and appointments:

# models/user_appointment.rb
class UserAppointment < ActiveRecord::Base
  belongs_to :user
  belongs_to :appointment
end

# models/appointment.rb
class Appointment < ActiveRecord::Base
  has_many :user_appointments
  has_many :users, :through => :user_appointments
end

# models/user.rb
class User < ActiveRecord::Base
  has_many :user_appointments
  has_many :appointments, :through => :user_appointments
end

Of course, you’ll probably also want to represent the owner of the appointment. You could expand your Appointment model to reflect who actually owns it. You could provide a relationship field in UserAppointment to describe whether a user is an owner or subscriber, but it might be easier to simply add a belongs_to relationship to the appointment model:

# models/appointment.rb
class Appointment < ActiveRecord::Base
  has_many :user_appointments
  has_many :users, :through => :user_appointments
  belongs_to :owner, :class_name => 'User'
end