rails 5 has_many through order on through table

Question

I want to order a has_many through relationship on a column in the through table

class DoctorProfile
  has_many :doctor_specialties
  has_many :specialties, through: :doctor_specialties

class Specialty
  has_many :doctor_specialties
  has_many :doctor_profiles, through: :doctor_specialties

class DoctorSpecialty
  belongs_to :doctor_profile
  belongs_to :specialty

I'd like the doctor specialties to be ordered by the column ordinal on DoctorSpecialty. Specifically this error happens when using includes

DoctorProfile.includes(:specialties).all

I've tried

has_many :specialties, -> { order 'doctor_specialties.ordinal' }, through: :doctor_specialties

DoctorProfile Load (0.6ms)  SELECT  "doctor_profiles".* FROM "doctor_profiles" ORDER BY "doctor_profiles"."id" ASC LIMIT $1  [["LIMIT", 1]]
  DoctorSpecialty Load (0.8ms)  SELECT "doctor_specialties".* FROM "doctor_specialties" WHERE "doctor_specialties"."doctor_profile_id" = 1
  Specialty Load (0.4ms)  SELECT "specialties".* FROM "specialties" WHERE "specialties"."id" = 69 ORDER BY doctor_specialties.ordinal

and receieve a missing FROM -clause error PG::UndefinedTable: ERROR: missing FROM-clause entry for table "doctor_specialties"

How can I define the order on the through table so specialties are returning in ascending order?

Note:

I was able to get this working by adding a default_scope to DoctorSpecialty

default_scope { order('ordinal ASC') }

However, I'm still wondering if there is a way to do it on the has_many through

Answer 1

I was able to get it working using

class DoctorProfile
    has_many :specialties, -> { order 'doctor_specialties.ordinal' }, through: :doctor_specialties

end

class DoctorSpecialty < ApplicationRecord
  belongs_to :doctor_profile
  belongs_to :specialty

  default_scope { order('ordinal ASC') }

end

Answer 2

Not sure if this is what's causing your error but you haven't completed the has many through relationship on the Specialty side. Should be has_many :doctor_profiles, through: :doctor_specialties

Also for this line in DoctorProfiles has_many :specialties, through: doctor_specialties, doctor_specialties needs to be a symbol

As for the ordering I think you need to do a joins instead of an includes

like DoctorProfile.joins(:doctor_specialties).order("doctor_specialties.ordinal ASC")