Rails Active Record，从has_many：through关系中获取相关记录，并且where子句通过

Question

I have a relationship set up with a has_many :through .

class Physician < ActiveRecord::Base
  has_many :appointments
  has_many :patients, through: :appointments
end

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

  # physician_id, patient_id
end


class Patient < ActiveRecord::Base
  has_many :appointments
  has_many :physicians, through: :appointments
end

How can I get all patients for a given physician where the appointment's role is equal to PI or G2?

I've tried Physician.find(50).appointments.where('role = ? or role = ?', 'PI', 'G2').patients

Edit:

I'm getting undefined method from the above. Shouldn't I be able to get the through's related records? In Physician.find(50).appointments.where('role = ? or role = ?', 'PI', 'G2') there should be an appointments method but there is not.

Answer 1

Since you want Patient objects back, start with that model. You want to add WHERE clauses on both Appointments and Physicians, so join on those associations. Use the Hash form of where to reference the joined tables.

Patient.joins(:physician).
  joins(:appointments).
  where(appointments: {role: ["PI", "G2"]}).
  where(physicians: {id: physician_id}).uniq

Update

Consider adding scopes to your models that you can reuse:

class Patient < ActiveRecord::Base
  scope :for_physician, ->(physician_id) do
    joins(:physicians).
    where(physicians: {id: physician_id}
  end

  scope :for_roles, ->(roles) do
    joins(:appointments).
    merge(Appointment.for_roles(roles))
  end
end

class Appointment < ActiveRecord::Base
  scope :for_roles, ->(roles) do
    where(role: roles)
  end
end

Then you can put them together like this

Patient.for_physician(50).for_roles(["PI", "G2"]).uniq