rails--rails/activerecord/lib/active_record/validations.rb

module ActiveRecord
  # Raised by <tt>save!</tt> and <tt>create!</tt> when the record is invalid.  Use the
  # +record+ method to retrieve the record which did not validate.
  #   begin
  #     complex_operation_that_calls_save!_internally
  #   rescue ActiveRecord::RecordInvalid => invalid
  #     puts invalid.record.errors
  #   end
  class RecordInvalid < ActiveRecordError
    attr_reader :record
    def initialize(record)
      @record = record
      super("Validation failed: #{@record.errors.full_messages.join(", ")}")
    end
  end

  module Validations
    def self.included(base) # :nodoc:
      base.extend ClassMethods

      base.class_eval do
        alias_method_chain :save, :validation
        alias_method_chain :save!, :validation
      end
    end

    module ClassMethods
      # Creates an object just like Base.create but calls save! instead of save
      # so an exception is raised if the record is invalid.
      def create!(attributes = nil, &block)
        if attributes.is_a?(Array)
          attributes.collect { |attr| create!(attr, &block) }
        else
          object = new(attributes)
          yield(object) if block_given?
          object.save!
          object
        end
      end
    end
    
    # The validation process on save can be skipped by passing false. The regular Base#save method is
    # replaced with this when the validations module is mixed in, which it is by default.
    def save_with_validation(perform_validation = true)
      if perform_validation && valid? || !perform_validation
        save_without_validation
      else
        false
      end
    end

    # Attempts to save the record just like Base#save but will raise a RecordInvalid exception instead of returning false
    # if the record is not valid.
    def save_with_validation!
      if valid?
        save_without_validation!
      else
        raise RecordInvalid.new(self)
      end
    end

    # Returns the Errors object that holds all information about attribute error messages.
    def errors
      @errors ||= Errors.new(self)
    end
  end
end