neutron-lib/doc/source/devref/api_converters.rst

API Converters

Definitions for REST API attributes, can include conversion methods to help normalize user input or transform the input into a form that can be used.

Defining A Converter Method

By convention, the name should start with convert_to_, and will take a single argument for the data to be converted. The method should return the converted data (which, if the input is None, and no conversion is performed, the implicit None returned by the method may be used). If the conversion is impossible, an InvalidInput exception should be raised, indicating what is wrong. For example, here is one that converts a variety of user inputs to a boolean value. :

def convert_to_boolean(data):
     if isinstance(data, six.string_types):
         val = data.lower()
         if val == "true" or val == "1":
             return True
         if val == "false" or val == "0":
             return False
     elif isinstance(data, bool):
         return data
     elif isinstance(data, int):
         if data == 0:
             return False
         elif data == 1:
             return True
     msg = _("'%s' cannot be converted to boolean") % data
     raise n_exc.InvalidInput(error_message=msg)

Using Validators

In client code, the conversion can be used in a REST API definition, by specifying the name of the method as a value for the 'convert_to' key on an attribute. For example:

'admin_state_up': {'allow_post': True, 'allow_put': True,
                   'default': True,
                   'convert_to': conversions.convert_to_boolean,
                   'is_visible': True},

Here, the admin_state_up is a boolean, so the converter is used to take user's (string) input and transform it to a boolean.

Test The Validator

Do the right thing, and make sure you've created a unit test for any converter that you add to verify that it works as expected.