rails has many association get latest record based on enum

I have a model as:

class Patient < ActiveRecord::Base
  has_many :patient_statuses

Another model as:

class PatientStatus < ActiveRecord::Base
  belongs_to :patient

  enum status: [:registered, :pending, :check_up, :admitted, :discharged]

Now, I want to get all the Patient whose last status is admitted


I think could do something like this:

class Patient < ActiveRecord::Base
  has_one  :current_status, -> 
    { order(created_at: :desc).limit(1) }, class_name: 'PatientStatus'

  def self.admitted
      patient_statuses: { status: 'admitted' }).references(:current_status)

You would call this scope method like this:


You could also create a scope that accepts an argument and get Patients based on any status:

def self.with_status(status)
    patient_statuses: { status: status }).references(:current_status)


Note that this code is provided as an example and might require some tweaking because of your enum attribute.

Please try this:

ids = PatientStatus.group('user_id', 'id').having('created_at = MAX(created_at)').where(status: :admitted).map(&:user_id).uniq
patients = Patient.where(id: ids)

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