validate_unique() is not enforced during API validation

[lampwins]

Environment

• Python version: 3.7
• NetBox version: 2.7.10

Steps to Reproduce

1. Create a virtualization cluster
2. In the API, create a VM with the name "vm1" and assigned to the cluster in step 1
3. In the API, create a second VM with the same name "vm1" and assigned to the same cluster from step 1

Expected Behavior

The unique constraint placed on VM name, cluster, and tenant should prevent the second VM from being created. This is true in the web UI.

Observed Behavior

The API validation ignores this unique constraint because of our use of validate_unique() on the virtual machine model. Django's ModelForm class does account for calling validate_unique() but we have implemented our own model validation in the API by way of ValidatedModelSerializer and it does not make a call to validate_unique(). We just need to call instance.validate_unique() after instance.clean()

[lampwins]

To clarify, the reason the unique constraint is "ignored" is because in NULL != NULL in unique comparisons which is why we have to implement validate_unique() in the first place to account for the possible null tenant field.