old_contents: from sqlalchemy.orm.exc import NoResultFound
  
  from wtforms import ValidationError
  
  
  class Unique(object):
      """
          Checks field value unicity against specified table field.
  
          :param get_session:
              A function that return a SQAlchemy Session.
          :param model:
              The model to check unicity against.
          :param column:
              The unique column.
          :param message:
              The error message.
      """
      field_flags = ('unique', )
  
      def __init__(self, db_session, model, column, message=None):
          self.db_session = db_session
          self.model = model
          self.column = column
          self.message = message
  
      def __call__(self, form, field):
          try:
              obj = (self.db_session.query(self.model)
                     .filter(self.column == field.data)
                     .one())
  
              if not hasattr(form, '_obj') or not form._obj == obj:
                  if self.message is None:
                      self.message = field.gettext(u'Already exists.')
                  raise ValidationError(self.message)
          except NoResultFound:
              pass
  
new_contents: from sqlalchemy.orm.exc import NoResultFound
  
  from wtforms import ValidationError
  
  
  class Unique(object):
      """
          Checks field value unicity against specified table field.
  
          :param get_session:
              A function that return a SQAlchemy Session.
          :param model:
              The model to check unicity against.
          :param column:
              The unique column.
          :param message:
              The error message.
      """
      field_flags = ('unique', )
  
      def __init__(self, db_session, model, column, message=None):
          self.db_session = db_session
          self.model = model
          self.column = column
          self.message = message
  
      def __call__(self, form, field):
          try:
              obj = (self.db_session.query(self.model)
                     .filter(self.column == field.data)
                     .one())
  
              print "VALIDATE", getattr(form, field)
              if self.message is None:
                  self.message = field.gettext(u'Already exists.')
              raise ValidationError(self.message)
          except NoResultFound:
              pass
  
subject: Update validators.py