How to use ActiveAdmin on models using has_many through association?

In answer tomblomfield follow up question in comments:

Try the following in your AA ActiveAdmin.register Model do block:

  controller do
    def scoped_collection
      YourModel.includes(:add_your_includes_here)
    end
  end

This should lazy load all your associations for each index page in a separate query

HTH

For 1)

show do
  panel "Patients" do
    table_for physician.appointments do
      column "name" do |appointment|
        appointment.patient.name
      end
      column :appointment_date
    end
  end
end

For 2)

form do |f|
  f.inputs "Details" do # physician's fields
    f.input :name
  end

  f.has_many :appointments do |app_f|
    app_f.inputs "Appointments" do
      if !app_f.object.nil?
        # show the destroy checkbox only if it is an existing appointment
        # else, there's already dynamic JS to add / remove new appointments
        app_f.input :_destroy, :as => :boolean, :label => "Destroy?"
      end

      app_f.input :patient # it should automatically generate a drop-down select to choose from your existing patients
      app_f.input :appointment_date
    end
  end
end