Fixes #150: Fix recalculation of cable paths when merging a branch with cable changes

[jeremystretch]

Fixes: #150

NOTE: This must be tested against the 20241-cable-change-records branch of NetBox, as it depends on changes made therein.

• Call a model's custom serialize_object() and deserialize_object() methods if defined
• Extend update_object() to support assigning non-field attributes

[jnovinger]

Approving this as is, as it fixes the issue. However, I did point out what I thought was a potential edge-case worth handling.

[jnovinger]

Ah, one thing I just noticed, in testing the reproduction steps from this comment, the diff/change counts don't match in different parts of the branch detail view.

[jnovinger]

Ah, one thing I just noticed, in testing the reproduction steps from this comment, the diff/change count don't match in different parts of the branch detail view.

Testing other scenarios, including the STR from the original ticket, did not produce the same behavior. For instance, in the case of changing the termination on one end of the existing cable (created in main) in the test branch showed 5 changes/diffs in all spots.

[jeremystretch]

The reason we're only seeing five changes after merging the branch is that the ObjectChange record resulting from the sixth and final change application shows the same pre- and post-change values for the A & B terminations; no ObjectChange record is recorded in main (unless CHANGELOG_SKIP_EMPTY_CHANGES is set to True).

I'm not sure there's a reasonable way to work around this, because in this case we can't compare to the instance's original state as we normally would under Cable's save() method.