Adding and removing from a has_many :through relation

From the Rails associations guide, they demonstrate a many-to-many relationship using has_many :through like so:

class Physician < ActiveRecord::Base
  has_many :appointments
  has_many :patients, :through => :appointments

class Appointment < ActiveRecord::Base
  belongs_to :physician
  belongs_to :patient

class Patient < ActiveRecord::Base
  has_many :appointments
  has_many :physicians, :through => :appointments

How would I create and remove appointments?

If I’ve got a @physician, do I write something like the following for creating an appointment?

@patient = params[:patient]
@physician.patients << @patient # Is this line needed?

What about code for deleting or destroying? Also, if a Patient no longer existed in the Appointment table will it get destroyed?

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  • One Solution collect form web for “Adding and removing from a has_many :through relation”

    In your code of creating an appointment, the second line is not needed, and using #build method instead of #new:

    @patient = params[:patient]  # yes, it worked

    For destroying an appointment record you could simply find it out and destroy:

    @appo = @physician.appointments.find(1)

    If you want to destroy the appointment records along with destroying a patient, you need to add the :dependency setting to has_many:

    class Patient < ActiveRecord::Base
      has_many :appointments
      has_many :physicians, :through => :appointments, :dependency => :destroy
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