Module ActiveRecord::Validations
In: vendor/rails/activerecord/lib/active_record/validations.rb

Active Records implement validation by overwriting Base#validate (or the variations, validate_on_create and validate_on_update). Each of these methods can inspect the state of the object, which usually means ensuring that a number of attributes have a certain value (such as not empty, within a given range, matching a certain regular expression).

Example:

  class Person < ActiveRecord::Base
    protected
      def validate
        errors.add_on_empty %w( first_name last_name )
        errors.add("phone_number", "has invalid format") unless phone_number =~ /[0-9]*/
      end

      def validate_on_create # is only run the first time a new object is saved
        unless valid_discount?(membership_discount)
          errors.add("membership_discount", "has expired")
        end
      end

      def validate_on_update
        errors.add_to_base("No changes have occurred") if unchanged_attributes?
      end
  end

  person = Person.new("first_name" => "David", "phone_number" => "what?")
  person.save                         # => false (and doesn't do the save)
  person.errors.empty?                # => false
  person.errors.count                 # => 2
  person.errors.on "last_name"        # => "can't be empty"
  person.errors.on "phone_number"     # => "has invalid format"
  person.errors.each_full { |msg| puts msg }
                                      # => "Last name can't be empty\n" +
                                           "Phone number has invalid format"

  person.attributes = { "last_name" => "Heinemeier", "phone_number" => "555-555" }
  person.save # => true (and person is now saved in the database)

An Errors object is automatically created for every Active Record.

Please do have a look at ActiveRecord::Validations::ClassMethods for a higher level of validations.

Methods

Classes and Modules

Module ActiveRecord::Validations::ClassMethods

Constants

VALIDATIONS = %w( validate validate_on_create validate_on_update )

Public Instance methods

Returns the Errors object that holds all information about attribute error messages.

[Source]

     # File vendor/rails/activerecord/lib/active_record/validations.rb, line 977
977:     def errors
978:       @errors ||= Errors.new(self)
979:     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.

[Source]

     # File vendor/rails/activerecord/lib/active_record/validations.rb, line 932
932:     def save_with_validation(perform_validation = true)
933:       if perform_validation && valid? || !perform_validation
934:         save_without_validation
935:       else
936:         false
937:       end
938:     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.

[Source]

     # File vendor/rails/activerecord/lib/active_record/validations.rb, line 942
942:     def save_with_validation!
943:       if valid?
944:         save_without_validation!
945:       else
946:         raise RecordInvalid.new(self)
947:       end
948:     end

Updates a single attribute and saves the record without going through the normal validation procedure. This is especially useful for boolean flags on existing records. The regular update_attribute method in Base is replaced with this when the validations module is mixed in, which it is by default.

[Source]

     # File vendor/rails/activerecord/lib/active_record/validations.rb, line 953
953:     def update_attribute_with_validation_skipping(name, value)
954:       send(name.to_s + '=', value)
955:       save(false)
956:     end

Runs validate and validate_on_create or validate_on_update and returns true if no errors were added otherwise false.

[Source]

     # File vendor/rails/activerecord/lib/active_record/validations.rb, line 959
959:     def valid?
960:       errors.clear
961: 
962:       run_validations(:validate)
963:       validate
964: 
965:       if new_record?
966:         run_validations(:validate_on_create)
967:         validate_on_create
968:       else
969:         run_validations(:validate_on_update)
970:         validate_on_update
971:       end
972: 
973:       errors.empty?
974:     end

Protected Instance methods

Overwrite this method for validation checks on all saves and use Errors.add(field, msg) for invalid attributes.

[Source]

     # File vendor/rails/activerecord/lib/active_record/validations.rb, line 983
983:       def validate #:doc:
984:       end

Overwrite this method for validation checks used only on creation.

[Source]

     # File vendor/rails/activerecord/lib/active_record/validations.rb, line 987
987:       def validate_on_create #:doc:
988:       end

Overwrite this method for validation checks used only on updates.

[Source]

     # File vendor/rails/activerecord/lib/active_record/validations.rb, line 991
991:       def validate_on_update # :doc:
992:       end

[Validate]