old-roraccounting/app/models/homie.rb

class Homie < ApplicationRecord
  has_many :money_moves_from, class_name: 'MoneyMove', foreign_key: :from_homie_id
  has_many :money_moves_to, class_name: 'MoneyMove', foreign_key: :to_homie_id

  def self.cash(importance)
    got = Homie.all.joins(:money_moves_to).group(:id).order(:id).sum(:amount)
    owe = Homie.all.joins(:money_moves_from).group(:id).order(:id).sum(:amount)

    result = [] 
    Homie.where(["importance > ?", importance]).map do |homie|
      total = got.fetch(homie.id, 0) - owe.fetch(homie.id,0)
      { homie: homie, amount: total } 
    end
  end
end