11432 device field

[arthanson]

Fixes: #11432

Makes the device field for interface read-only if a patch request. The 'normal' way of doing this would be by override get_extra_kwargs, but that doesn't work if the field is explicitly declared (which this is). As read-only it is just ignored if the patch is done which is the DRF convention.

[jeremystretch]

This may be better addressed in the model itself. I know the bug was opened specifically for the API, however it's something we should prevent via other means as well. Once an interface has been assigned a PK, its assigned device should not be allowed to change.

[kkthxbye-code]

The intention was to match the UI, which only allows reassigning the device of InventoryItem, but not the other device components listed here:

'ConsolePort',
'ConsoleServerPort',
'DeviceBay',
'FrontPort',
'Interface',
'ModuleBay',
'PowerOutlet',
'PowerPort',
'RearPort',

[arthanson]

@jeremystretch should be ready now, tests fixed.

[jeremystretch]

Can we simplify this a bit by doing something like this? Also, I'd really like to avoid introducing a new public method on the serializer as it could result in confusion.

Suggested change

	class BaseReadonlyDeviceMixin:
	def get_fields(self, *args, **kwargs):
	fields = super().get_fields(*args, **kwargs)
	# get_extra_kwargs doesn't work if field explicitly declared on serializer...
	if (self.instance):
	fields[self.get_field_name()].read_only = True
	return fields
	class ReadonlyDeviceMixin(BaseReadonlyDeviceMixin):
	# can't be a field as mucks up serializer
	def get_field_name(self):
	return "device"
	class ReadonlyDeviceTypeMixin(BaseReadonlyDeviceMixin):
	def get_field_name(self):
	return "device_type"
	class ReadonlyDeviceMixin:
	_field_name = 'device'
	def get_fields(self, *args, **kwargs):
	fields = super().get_fields(*args, **kwargs)
	if self.instance:
	fields[self._field_name].read_only = True
	return fields
	class ReadonlyDeviceTypeMixin(ReadonlyDeviceMixin):
	_field_name = 'device_type'

[jeremystretch]

I think this still needs to be addressed in the model. With the field set to read-only, any attempt to change the parent device/device type of an existing component is silently ignored, because the field is ignored. However, any other valid attributes in the request will be applied successfully. I think we should instead return a validation error, so that the client is aware the entire proposed change did not succeed.

[arthanson]

@jeremystretch changed to model based validator, as discussed this will not be officially correct in the OpenAPI spec. Looked at doing it as read_only in the serializer and overriding validate_device, but that is never called if read_only is set. Can also be done fairly cleanly in the validate_device if no read_only is set, but that will only address it for the API call and you had mentioned wanting at model level so moved it there.