'Post-process to create or update records. Called during POST
before validation of the outer form.
To be implemented in subclass.
@param value: the value from the form (as JSON)
@return: tuple (record_id, error)'

def postprocess(self, value):

    (values, error) = self.validate(value)
    if values:
        record_id = values.get('id')
    else:
        record_id = None
    if error:
        return (None, error)
    return (record_id, None)
