Fixes: #14606 - For Cable API add PK for cable terminations to serializer

[DanSheps]

Fixes: #14606

• Add pk field for cable termination
• Add test

[jeremystretch]

This one is probably a bit stickier than I realized in the original bug report.

We should really be using a nested CableTerminationSerializer here, omitting its cable and cable_end fields (as they're redundant in this context). That would address the primary issue.

However, the catch is that the generic serializer currently in use returns the fields object_type, object_id and object, whereas CableTerminationSerializer returns termination_type, termination_id, and termination. Swapping out the serializer would be a breaking change.

We could address this in v4.1, however I'm hesitant to slip in a breaking change so late in the beta period. For now, we could settle with just adding the id field to GenericObjectSerializer, and capture this as a potential change for v4.2.

[jeremystretch]

This doesn't require a new serializer: We can just add the id field to GenericObjectSerializer.

[DanSheps]

Unfortunately since a_terminations/b_terminations is a property function that includes the actual termination (Interface/CircuitTermination/etc) and not the CableTermination object it won't be the proper id (it will be the interface id for example, not the cable termination id).

This is why I opted to go this route, as as you mention, it would be a breaking change. Perhaps we should aim for 4.1 instead and I just rebase and swap the serializer.

It may also make more sense to maintain a_terminations/b_terminations as is (add ID however to GenericObjectSerializer still) and add a generic "terminations" which operates on Cable.terminations which is I think where it would be appropriate to use the CableTermination serializer.

[DanSheps]

• Rebased to feature
• Modified serializer to add terminations related objects

Let me know if you would rather replace a_terminations / b_terminations (will be non-trivial as they currently only return the Terminated Objects (Interface, etc)

[jeremystretch]

This is going to be more involved than I originally anticipated, because the a_terminations and b_terminations attributes of a cable instance are populated with the actual terminating objects, rather than CableTermination instances. We don't want to just tack these on in addition to the existing attributes because that would be redundant and inefficient. We'll have to explore our options, which likely include tweaking the underlying querysets for the Cable model.

[jeremystretch]

Appreciate your work on this @DanSheps. I'm going to close it out for now; let's re-evaluate our options for a potential change in v4.2.