def get_expand(self, prop_or_name):
"""Get a Model instance associated with an expanded property.
Args:
prop_or_name: Property or str, The expandable property (or property name)
that should be expanded.
Returns:
If expanded data is present, an instance of the Model listed in the
property's `expands_to` attribute.
Else, None.
Raises:
PropertyError: An invalid or non-expandable property was provided OR the
expands_to attribute on the property did not correspond to a known
Model kind.
"""
prop = self._get_and_validate_property(prop_or_name,
require_expandable=True)
expand_cls = self._KIND_MAP.get(prop.expands_to)
if expand_cls is None:
raise excs.PropertyError('Cannot expand to unknown Model "%s"' %
prop.expands_to)
expanded_properties = (key for key in self._obj_dict.keys()
if key.startswith(prop.name + '_'))
if any(expanded_properties):
return expand_cls.from_dict(self._obj_dict, prefix=prop.name)
else:
return None
def _get_and_validate_property(cls,
prop_or_name,
require_updatable=False,
require_expandable=False):
"""Converts the arg to a Property and ensures it's valid.
Args:
prop_or_name: Property or str, If str, it should be the name of a property
on this Model. If Property, the function will verify that it belongs
to this Model class.
require_updatable: bool, Whether to perform an additional validation step
to ensure the returned property is able to be updated.
require_expandable: bool, Whether to perform an additional validation step
to ensure the returned property is able to be expanded.
Returns:
The Property object provided or the one associated with the name that was
provided.
Raises:
PropertyError: Some aspect of validation failed.
"""
if isinstance(prop_or_name, Property):
prop = prop_or_name
else:
prop = cls._PROPERTIES.get(prop_or_name)
if prop is None:
raise excs.PropertyError(
'Unknown property: {}'.format(prop_or_name))
if not cls.is_valid_property(prop):
raise excs.PropertyError('{} cannot be used with {}'.format(
prop, cls.__name__))
elif require_updatable and not prop.updatable:
raise excs.PropertyError(
'Property {} may not be updated'.format(prop))
elif require_expandable and not prop.expandable:
raise excs.PropertyError(
'Property {} may not be expanded'.format(prop))
return prop