old-zsterminator/app/models/reservation.rb

class Reservation < ApplicationRecord
  belongs_to :company
  belongs_to :customer
  belongs_to :team

  validates :company_id, presence: true
  validates :customer_id, presence: true
  validates :team_id, presence: true
end

class ReservationSerializer < ActiveModel::Serializer
  attributes :id, :company, :customer, :team, :start_time, :end_time
end