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 944
944:     def errors
945:       @errors ||= Errors.new(self)
946:     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 899
899:     def save_with_validation(perform_validation = true)
900:       if perform_validation && valid? || !perform_validation
901:         save_without_validation
902:       else
903:         false
904:       end
905:     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 909
909:     def save_with_validation!
910:       if valid?
911:         save_without_validation!
912:       else
913:         raise RecordInvalid.new(self)
914:       end
915:     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 920
920:     def update_attribute_with_validation_skipping(name, value)
921:       send(name.to_s + '=', value)
922:       save(false)
923:     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 926
926:     def valid?
927:       errors.clear
928: 
929:       run_callbacks(:validate)
930:       validate
931: 
932:       if new_record?
933:         run_callbacks(:validate_on_create)
934:         validate_on_create
935:       else
936:         run_callbacks(:validate_on_update)
937:         validate_on_update
938:       end
939: 
940:       errors.empty?
941:     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 950
950:       def validate #:doc:
951:       end

Overwrite this method for validation checks used only on creation.

[Source]

     # File vendor/rails/activerecord/lib/active_record/validations.rb, line 954
954:       def validate_on_create #:doc:
955:       end

Overwrite this method for validation checks used only on updates.

[Source]

     # File vendor/rails/activerecord/lib/active_record/validations.rb, line 958
958:       def validate_on_update # :doc:
959:       end

[Validate]