Circuit Termination with A and Z Swap broken with 1.3.x

[smk4664]

Environment

• Nautobot version (Docker tag too if applicable): 1.3.1
• Python version: 3.8
• Database platform, version:
• Middleware(s):

Steps to Reproduce

1. Create a Circuit with two terminations
2. Click the Swap termination button.

Expected Behavior

The terminations will swap sides.

Observed Behavior

Server Error: Circuit has no field named 'termination__'

[smk4664]

Notice the termination__ is two underscores. In order to avoid a Unique Constraint issue when performing the swap, we set the term_side to _, but when we call save, it is getting picked up by signals.py where the circuit gets filtered by termination__:

    fields = {
        "last_updated": timezone.now(),
        f"termination_{instance.term_side.lower()}": instance.pk,
    }
    Circuit.objects.filter(pk=instance.circuit_id).update(**fields)

[smk4664]

Also, unfortunately there are no tests for the CircuitSwapTerminations, so this did not get caught by tests.

[glennmatthews]

Looks to have been introduced by #1144. Appears that a similar regression was fixed in NetBox by netbox-community/netbox@a4955b4.