ChainedFieldsMixin fails to restrict queryset when form validation fails

[jeremystretch]

Environment

• Python version: 3.5.2
• NetBox version: 2.5.10

Steps to Reproduce

1. Bulk create a large number of IP addresses. 50K seems to be sufficient to replicate using the development server.
2. Create a new VRF named "MyVRF" and ensure "Enforce unique space" is selected
3. Create a new IP address 192.0.2.1/32 assigned to MyVRF
4. Attempt to create a second new IP address192.0.2.1/32 assigned to MyVRF

Expected Behavior

The creation should fail and immediately return the form with the original data and a validation error.

Observed Behavior

NetBox takes a very long time to return the response. (With debugging enabled, it never returns.) I believe what's happening is that ChainedFieldsMixin is not filtering the queryset of the nat_inside field due to the failed form validation. This means the field is rendered with the queryset IPAddress.objects.all(), which will take a long time to render when a large number of IPAddress objects exist.

I still need to dig into this some more, but I wanted to make sure the bug was captured. We should also give some more though to how chained fields work in general now that the form widgets are all API-driven.

[hellerve]

I don’t know how to fix this, but I wanted to chime in to corroborate your hunch: the nat_inside field is in fact not being filtered! I dug into the mixin to figure out how it works, but I’m not quite sure I understand the rules around it; anyway, at least I can say that looking at the code under a debugger, filters_dict is in fact not updated.