Deleting DeviceType with Component raises DeviceType.DoesNotExist exception

[rodvand]

Environment

• Python version: 3.6.8
• NetBox version: 2.6.11

Steps to Reproduce

1. Create a Device Type
2. Add any component to the device type template (example two Power ports)
3. Delete the Device Type

Expected Behavior

The Device Type to be deleted and being redirected to the Device Type list.

Observed Behavior

The Device Type is deleted, but an exception is raised:

<class 'dcim.models.DeviceType.DoesNotExist'>

DeviceType matching query does not exist.

The URL with the exception is https://netbox-server/dcim/device-types/3/delete/

It seems like deleting the device type components are trying to redirect to the Device Type after deletion, but the Device Type has already been deleted. So some way of differentiating the return_url when deleting the Device Type (which includes deleting all components) contra when deleting only components from the Device Type is needed.

[jeremystretch]

The root issue here is that the component template(s) are being deleted after the parent device type. When NetBox attempts to record a changelog entry for the deletion of the component templates, an exception is raised because the parent DeviceType instance no longer exists. Other models in NetBox (e.g. devices) appear to be affected by this bug as well.

I'll need to take more time to dig into this. It's not sufficient to simply nullify the parent field as we need to ensure the relationship is recorded in the changelog.

[hSaria]

By that, you're also referring to other instances of ObjectChange, right?

[jeremystretch]

What I mean is that the ObjectChange that gets created in response to the deletion of a component template must be associated with the template's parent DeviceType.

This is assuming we continue recording ObjectChanges for related items during deletion events. I've been wondering lately if there's any real reason to do so. Omitting them would greatly speed up deletion actions where there are many related objects (e.g. deleting a device with hundreds of interfaces). That's a separate discussion though.