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Validatable is a library for adding validations.

Created by Jay Fields, updated by John Nunemaker


$ gem install jnunemaker-validatable -s


You may use, copy and redistribute this library under the same terms as Ruby itself (see


Validation of an entire hierarchy of objects with errors aggregated at the root object.

class Person include Validatable validates_presence_of :name attr_accessor :name end

class PersonPresenter include Validatable include_validations_for :person attr_accessor :person

def initialize(person) @person = person end end

presenter = presenter.valid? #=> false presenter.errors.on(:name) #=> “can't be blank”

Validations that turn off after X times of failed attempts.

class Person include Validatable validates_presence_of :name, :times => 1 attr_accessor :name end

person = person.valid? #=> false person.valid? #=> true

Validations can be given levels. If a validation fails on a level the validations for subsequent levels will not be executed.

class Person include Validatable validates_presence_of :name, :level => 1, :message => “name message” validates_presence_of :address, :level => 2 attr_accessor :name, :address end

person = person.valid? #=> false person.errors.on(:name) #=> “name message” person.errors.on(:address) #=> nil

Validations can also be given groups. Groups can be used to validate an object when it can be valid in various states. For example a mortgage application may be valid for saving (saving a partial application), but that same mortgage application would not be valid for underwriting. In our example a application can be saved as long as a Social Security Number is present; however, an application can not be underwritten unless the name attribute contains a value.

class MortgageApplication
  include Validatable
  validates_presence_of :ssn, :groups => [:saving, :underwriting]
  validates_presence_of :name, :groups => :underwriting
  attr_accessor :name, :ssn

application =
application.ssn = 377990118
application.valid_for_saving? #=> true
application.valid_for_underwriting? #=> false

As you can see, you can use an array if the validation needs to be part of various groups. However, if the validation only applies to one group you can simply use a symbol for the group name.

Similar to Rails, Validatable also supports conditional validation.

class Person include Validatable attr_accessor :name validates_format_of :name, :with => /.+/, :if => { !name.nil? } end #=> true Validatable also exposes an after_validate hook method.

class Person include Validatable validates_presence_of :name attr_accessor :name end class ValidatesPresenceOf after_validate do |result, instance, attribute| instance.errors.add(“#{attribute} can't be blank”) unless result end end

person = person.valid? #=> false person.errors.on(:name) #=> “name can't be blank” The after_validate hook yields the result of the validation being run, the instance the validation was run on, and the attribute that was validated

In the above example the attribute “name” is appended to the message.

See the tests for more examples


Rick Bradley, Anonymous Z, Jason Miller, Ali Aghareza, Xavier Shay, Dan Manges, Karthik Krishnan and Venkat, Clint Bishop, Chris Didyk, Yi Wen

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