Validation in all its glory¶

• Fields already provide their own valiation. eg: zope.schema.Int field should be integer, ...

• constrains if you need a little more control.

  from zope.interface import Invalid
  
  
  def over_21(value):
      if value >= 21:
          return True
      raise Invalid("You need to be over 21, to register.")
  
  class IPerson(form.Schema):
      ...
  
      age = schema.Int(
          title=u"Age",
          constraint=over_21,
          required=True)
  

• Validate widget using @form.validator

  @form.validator(field=IPerson['age'])
  def over_21(value):
      if value >= 21:
          return True
      raise Invalid("You need to be over 21, to register.")
  

  Possible to make validator more specific or generic using ‘context’, ‘request’, ‘view’, ‘field’, ‘widget’ parameter of @form.validator decorator.

• more advanced

  from z3c.form import validator
  
  
  class Over21(validator.SimpleFieldValidator):
  
      def validate(self, value):
          # here we could skipt default field validation
          super(Over21, self).validate(value)
  
          if value >= 21:
              return True
          raise Invalid("You need to be over 21, to register.")
  
  
  validation.WidgetValidatorDiscriminators(Over21,
              field=IPerson['age'], view=RegisterForm)
  grok.global_adapter(Over21)
  

  This we use in case:

  • want to skip default validation of field properties (‘required’, ‘min’, ..).
  • need to access context, request, form, field, widget to validate.

• invariants

  from zope.interface import invariants
  
  
  class IPerson(form.Schema):
      ...
  
      @invariants
      def legal_age(data):
          if data.city == 'Sevilla' and \
             data.age >= 18:
             return True
          elif data.age >= 21:
              return True
          raise Invalid("You need to be over 21, to register.")
  

• validation can also happen inside action handler

  from z3c.form.interfaces import ActionExecutionError
  from z3c.form.interfaces import WidgetActionExecutionError
  
  
  class RegisterForm(form.SchemaForm):
      ...
  
      def handleRegister(self, action):
          data, errors = self.extractData()
  
          if data['age'] > 150:
              raise WidgetActionExecutionError(
                          Invalid(u"nobody should register if its older then 100"))
  
          try:
              registration = getToolByName(self.context, 'portal_registration')
              registration.addMember(data['email'], '12345', properties=data)
          except ValueError, e:
              raise ActionExecutionError(
                      Invalid(u"User with this email already exists."))
  
          if errors:
              self.status = self.formErorrsMessage
              return
          ...
  

• replace only text in error message

  from zope.schema.interfaces import ValidationError
  
  @form.error_message(field=IPerson['age'], error=ValidationError)
  def to_young_message(value):
      return "By the law we are not allowed to let you in. Sorry." \
             "See you in %s years." % (21 - value)
  

  allowed arguments for error_message are:

  error, request, widget, field, form, contet

  standard errors are (all listed in zope.schema.interfaces):

  RequiredMissing, WrongType, TooBig, TooSmall, TooLong, TooShort, InvalidValue, ConstraintNotSatisfied, WrongContainedType, NotUnique, InvalidURI, InvalidId, InvalidDottedName

• output HTML

  import zope.component
  from z3c.form import error
  from zope.schema.interfaces import TooSmall
  
  
  TooYoung = error.ErrorViewMessage(
       u'Too young', error=TooSmall, field=IPerson['age'])
  
  zope.component.provideAdapter(TooYoung, name='message')