dev.log

Training Load (0.2ms)  SELECT `trainings`.* FROM `trainings` WHERE ((begin_at <= '2011-06-15 09:00:00' AND '2011-06-15 09:00:00' <= finish_at) 
 OR (begin_at <= '2011-06-15 11:00:00' AND '2011-06-15 11:00:00' <= finish_at))
Training Load (0.2ms)  SELECT `trainings`.* FROM `trainings` WHERE `trainings`.`trainer_id` = 3

training.rb

class Training < ActiveRecord::Base
  belongs_to :service
  belongs_to :trainer, :class_name => 'User'
  belongs_to :location

  has_many :participations
  has_many :participants, :through => :participations

  validate :validates_trainer_availability
  validate :validates_location_availability


  def self.between(begin_at, finish_at)
    Training.where(
      '(begin_at <= :begin_at AND :begin_at <= finish_at) 
      OR (begin_at <= :finish_at AND :finish_at <= finish_at)',
      :begin_at  => begin_at,
      :finish_at => finish_at
    )
  end


  private

  def validates_trainer_availability
    trainings = (Training.between(self.begin_at, self.finish_at) & Training.where(:trainer_id => trainer_id))
    errors.add(:trainer_id, :trainer_already_used) if trainings.any?
  end
  
  def validates_location_availability
  end
end