Moving cable endpoints

[candlerb]

I've just installed a new switch and moved about 2 dozen cables from the old one to the new one. This time, I really want to avoid the tedium of deleting cables and individually creating new ones, where everything is identical to the old one apart from one endpoint.

I am wondering: if I use nbshell or a custom script to change termination_a or termination_b and save back to the database, will this trigger all the necessary dependent changes? Specifically I'm thinking of the CablePath, and the various columns on the dcim_interface table from CableTerminatino and PathEndpoint (cable_id, _cable_peer_id, _cable_peer_type_id, _path_id)

Or would running manage.py trace_paths [--force] fix all these? From the code I expect that it would fix CablePath but I'm not sure about the attributes on Interface.

[jeremystretch]

#4881 is open and just waiting for a volunteer.

[candlerb]

It would certainly be nice to have this in the UI.

But for now my question remains: if I simply modify (one of) the endpoints on a Cable model instance, will all necessary changes propagate? And if not, would manage.py trace_paths be sufficient to correct everything?

(Aside: I haven't tried PATCHing the endpoints on a cable via the REST API. But it looks like this won't be allowed)

[candlerb]

In the end I solved this via CSV export and import, although some work is required because the formats are very different (#5952).

I made a new export template (which also turned up issue #7813):

side_a_device,side_a_type,side_a_name,side_b_device,side_b_type,side_b_name,type,status,label,color,length,length_unit
{%- for c in queryset %}
{%- if c.termination_a_type.app_label != 'circuits' and c.termination_b_type.app_label != 'circuits' %}
{{ c.termination_a.device.name }},{{ c.termination_a_type.app_labeled_name|replace(" | ",".")|replace(" ","") }},{{ c.termination_a.name }},{{ c.termination_b.device.name }},{{ c.termination_b_type.app_labeled_name|replace(" | ",".")|replace(" ","") }},{{ c.termination_b.name }},{{ c.type }},{{ c.status }},"{{ c.label }}",{{c.color}},{{ c.length|replace("None","") }},{{ c.length_unit }}
{%- endif %}
{%- endfor %}

Then a manual search-replace to change the endpoint device name and the port number format; delete the old cables; import the new cables.

[candlerb]

I am shortly about to have to move another whole bunch of cables from one device to another.

I am considering writing a custom script for this. But my question from before was unanswered:

if I use nbshell or a custom script to change termination_a or termination_b and save back to the database, will this trigger all the necessary dependent changes?

That is, is there any defined way in Python code to change a single cable endpoint, or would this leave the database in an inconsistent state? The model is too complex for me to understand all the potential knock-on effects.

[candlerb]

Ah, I think I found the answer in code:

    def clean(self):
...
        # If editing an existing Cable instance, check that neither termination has been modified.
        if self.pk:
            err_msg = 'Cable termination points may not be modified. Delete and recreate the cable instead.'

[grinapo]

I see all open issues were closed by the bot, so cannot comment there.
I see that simple editing was disabled due to problematic integrity keeping, and people are suggested to delete and recreate the cable.
This is suboptimal, as the physical cables are usually keeping all their attributes, and also usually one endpoint.

Would it be easier and possible to:

1. Provide an interface which would delete the cable, and pre-fill a new cable with the data of the old (just deleted) cable, which could be inserted? This would help individual cable moves. Or:
2. Make it possible to keep physical "dangling" cables, to be re-used in new connection? (← not so good solution, but would make it much simpler to pick one from the unused cables, which already have their properties set.)