In order to add a dynamic tab to a NetBox object, whether it's a core object(ex. Device, Device Type) or a user defined object we need a table to act as a map which states which kind of tab corresponds to which object. To do that we can define a Django model like this:

from django.db import models

class TabMap(models.Model):

    class Meta:
        constraints = [
            models.UniqueConstraint(fields=('object_type', 'object_id', 'tab'),
                                    name='unique_object_type_object_id_tab'),
        ]

    class Tab(models.TextChoices):
        CUSTOMTAB = 'CUSTOMTAB', 'Custom Tab'

    class ObjectType(models.TextChoices):
        DEVICE = 'Device', 'Device'

    object_type = models.CharField(max_length=30, choices=ObjectType.choices)
    object_id = models.PositiveIntegerField()
    tab = models.CharField(max_length=30, choices=Tab.choices)

As we can see TabMap has three fields which maps a specific object_id(ex. 2) which has a specific object_type(ex. Device) to a specific tab_id.

Then we need to register a tab with it's own template for the object type that we want to have the said tab:

from dcim.models import Device
from netbox.views import generic
from utilities.views import ViewTab, register_model_view

@register_model_view(Device, name='custom_tab')
class CustomDeviceTab(generic.ObjectView):
    template_name = 'my_netbox_plugin/custom_device_tab.html'
    tab = ViewTab(label='Custom Tab',
                  badge=has_tab(tab=TabMap.Tab.CUSTOMTAB),
                  weight=10000,
                  hide_if_empty=True)
    queryset = Device.objects.all()

In here using register_model_view decorator we specified that we want to create a tab for the Device object type and with a relative path of custom_tab(for example the tab's URL would be something like my-netbox-instance.net/dcim/devices/2/custom_tab/).

In template_name we specified that we want to use my_netbox_plugin/custom_device_tab.html as the template of our tab.

Finally using the tab field and NetBox's ViewTab class we can give a label, badge, weight(used for ordering the tab between the already present list of tabs, lower values push the tab to left while the higher values push it to the right) and lastly hide_if_empty(which hides the tab if it's badge doesn't have a meaningful value).

Also badge accepts a simple value like string or a callable with object's id as first argument like for example a function and as you can see in the above code snippet we have provided a function named has_tab which itself returns a function to be used by the badge field. The definition of the function is below:

def has_tab(tab):

    def get_badge_value(object):
        if TabMap.objects.filter(object_type=object.__class__.__name__,
                                 object_id=object.id,
                                 tab=tab).exists():
            return 'Custom Badge'

    return get_badge_value

has_tab accepts a tab(basically a value of the Tab enum we defined in TabMap Django model) and returns a function named get_badge_value which accepts an object id as object and returns a value as tab's badge if the tab has been registered for that object.

Ultimately we define a new view named register_tab with the responsibility of registering a tab for a certain object using the provided query strings: object_type, object_id and tab:

from django.http import HttpResponseRedirect

from . import models

def register_tab(request):
    object_type = request.GET.get('object_type')
    object_id = request.GET.get('object_id')
    tab = request.GET.get('tab')

    if object_type not in models.TabMap.ObjectType:
        raise Exception(
            f'Object Type: `{object_type}` is invalid, make sure that you have defined it in `ObjectType` enum'
        )
    if tab not in models.TabMap.Tab:
        raise Exception(
            f'Tab: `{tab}` is invalid, make sure that you have defined it in `Tab` enum'
        )

    models.TabMap.objects.get_or_create(object_type=object_type,
                                        object_id=object_id,
                                        tab=tab)

    return HttpResponseRedirect(request.META.get('HTTP_REFERER'))

Don't forget to register this view in your urls.py file:

from django.urls import path

from . import views

path('register_tab/', views.register_tab, name='register_tab')

Then in order to register the Custom Tab tab for a Device with the id of 2 we invoke this view like so:

<a href="{% url 'plugins:my_netbox_plugin:register_tab' %}?object_type={{ object_type.DEVICE }}&object_id={{ 2 }}&tab={{ tabs.CUSTOMTAB }}">Add Custom Tab</a>

Notice that in here we have passed Tab and ObjectType enums as extra context values tabs and object_type respectively.

Links

NetBox Documentation