Relationship Associations remain when associated objects are deleted

[pke11y]

Environment

• Python version: 3.8.5
• Nautobot version: v1.0.1

Steps to Reproduce

1. Create a many-to-many relationship between ipam.vlan and ipam.vlan_groups
2. Create multiple VLANs in site-X
3. Create a Vlan Group in site-X
4. Create associations by assigning VLANs to the VLAN Group
5. Delete the VLAN Group object

Relationship

        {
            "id": "f33aac1f-3b3c-4d35-89e4-a6a565a6594c",
            "url": "http://127.0.0.1/api/extras/relationships/f33aac1f-3b3c-4d35-89e4-a6a565a6594c/",
            "name": "vlan-vlangroup",
            "slug": "vlan-vlangroup",
            "description": "VLAN to VLAN Group mapping",
            "type": "many-to-many",
            "source_type": "ipam.vlan",
            "source_label": "",
            "source_hidden": false,
            "source_filter": {
                "site": "brq2"
            },
            "destination_type": "ipam.vlangroup",
            "destination_label": "",
            "destination_hidden": false,
            "destination_filter": null
        }

Expected Behavior

Any relationship associations including the deleted VLAN Group, should also be deleted.

Observed Behavior

All relationship associations remain in the database.

        {
            "id": "cb2f5c23-e323-4d6e-bf41-62be5ec30c26",
            "relationship": {
                "id": "f33aac1f-3b3c-4d35-89e4-a6a565a6594c",
                "url": "http://127.0.0.1/api/extras/relationships/f33aac1f-3b3c-4d35-89e4-a6a565a6594c/",
                "name": "vlan-vlangroup",
                "slug": "vlan-vlangroup",
                "display": "vlan-vlangroup"
            },
            "source_type": "ipam.vlan",
            "source_id": "15cda72f-bdb8-5d9c-88d8-17c6d5fdd979",
            "destination_type": "ipam.vlangroup",
            "destination_id": "fa0eecbd-fcc1-4435-9d44-72e31554f176"
        },

NOTE: no VLANs exist with the native 1:M mapping during the procedure.

The relationships are available to view on the UI. The VLAN Group target object is None on the UI.