has_many :through with counter_cache

Question

It is my understanding that when defining a :counter_cache option it is to be specified on the model that includes the belongs_to declaration. So I am a little unsure of how

Answer 1

I ran into a similar problem, counting the number of records in a two-deep relationship. In your example, this would be the number of Patients for a Physician, as opposed to the number of Appointments. (e.g. don't count multiple appointments for one patient) I haven't tested the other solutions offered, but it appears they return the number of appointments.

I found no way to do this in Rails 4, primarily because there is no belongs_to through: option. After exhausting several fruitless approaches, I found gem counter_culture. This solved the problem easily, by defining a two-deep relationship to be counted:

class Patient < ActiveRecord::Base
  belongs_to :appointment
  counter_culture [:appointment, :physician]
end

Add a counter field to Physician with:

rails generate counter_culture Physician patients_count

And voila! You can now do easy activerecord queries like:

Physician.order(patients_count: 'DESC')