Sum items in ruby on rails

Question

I am new in Ruby on Rails. This is my model but i don't know how solved.

class Recibo < ActiveRecord::Base
  attr_accessible :caja_id, 
  :doctor_id, 
  :numero_recibo, 
  :paciente_id, 
  :total,
  :total_porcentaje_doctor,
  :total_porcentaje_clinica,
  :total_porcentaje_laboratorio, 
  :servicio_ids

  belongs_to :caja
  belongs_to :doctor
  belongs_to :paciente

  has_many :atencions
  has_many :servicios, :through => :atencions

  before_save do
    servicio_by_id = Servicio.select("precio, 
      porcentaje_doctor, 
      porcentaje_clinica, 
      porcentaje_laboratorio").where(:id => servicio_ids).to_a

    self.total = servicio_by_id.sum(&:precio)

    self.total_porcentaje_doctor = servicio_by_id.sum(&(:porcentaje_doctor) * (:price))
    self.total_porcentaje_clinica = servicio_by_id.sum(&:porcentaje_clinica)
    self.total_porcentaje_laboratorio = servicio_by_id.sum(&:porcentaje_laboratorio)

  end

end

total is fine but total_porcentaje_doctor is not!

The error is:

undefined method `*' for :porcentaje_doctor:Symbol

Thanks!

Answer 1

It looks like you have some overhead for sum calculation, instead of loading all objects to memory you could just calculate sum on DB level and get results.

  scoped_sercvio = Servicio.where(:id => servicio_ids)
  self.total_porcentaje_clinica = scoped_sercvio.sum(:porcentaje_clinica)

You can even do nested calculation, such us multiplication on DB level. eg.

  self.total_porcentaje_doctor = scoped_sercvio.sum('porcentaje_doctor * price')

Robots wrote article about it, you could check it out here http://robots.thoughtbot.com/refactoring-ruby-iteration-patterns-to-the-database

Answer 2

Since you are making the calculation using two columns in the array I think you will need to write this line as:

self.total_porcentaje_doctor = servicio_by_id.sum { |x| (x.porcentaje_doctor * x.precio) }