9654 device weight (#10448)

* 9654 add weight fields to devices

* 9654 changes from code review

* 9654 change _abs_weight to grams

* Resolve migrations conflict

* 9654 code-review changes

* 9654 total weight on devices

* Misc cleanup

Co-authored-by: Jeremy Stretch <jstretch@ns1.com>

netbox/dcim/models/racks.py

@@ -1,4 +1,5 @@
 import decimal
+from functools import cached_property
 
 from django.apps import apps
 from django.contrib.auth.models import User
@@ -18,7 +19,8 @@ from utilities.choices import ColorChoices
 from utilities.fields import ColorField, NaturalOrderingField
 from utilities.utils import array_to_string, drange
 from .device_components import PowerPort
-from .devices import Device
+from .devices import Device, Module
+from .mixins import WeightMixin
 from .power import PowerFeed
 
 __all__ = (
@@ -62,7 +64,7 @@ class RackRole(OrganizationalModel):
         return reverse('dcim:rackrole', args=[self.pk])
 
 
-class Rack(NetBoxModel):
+class Rack(NetBoxModel, WeightMixin):
     """
     Devices are housed within Racks. Each rack has a defined height measured in rack units, and a front and rear face.
     Each Rack is assigned to a Site and (optionally) a Location.
@@ -185,7 +187,7 @@ class Rack(NetBoxModel):
 
     clone_fields = (
         'site', 'location', 'tenant', 'status', 'role', 'type', 'width', 'u_height', 'desc_units', 'outer_width',
-        'outer_depth', 'outer_unit',
+        'outer_depth', 'outer_unit', 'weight', 'weight_unit',
     )
 
     class Meta:
@@ -454,6 +456,22 @@ class Rack(NetBoxModel):
 
         return int(allocated_draw / available_power_total * 100)
 
+    @cached_property
+    def total_weight(self):
+        total_weight = sum(
+            device.device_type._abs_weight
+            for device in self.devices.exclude(device_type___abs_weight__isnull=True).prefetch_related('device_type')
+        )
+        total_weight += sum(
+            module.module_type._abs_weight
+            for module in Module.objects.filter(device__rack=self)
+            .exclude(module_type___abs_weight__isnull=True)
+            .prefetch_related('module_type')
+        )
+        if self._abs_weight:
+            total_weight += self._abs_weight
+        return round(total_weight / 1000, 2)
+
 
 class RackReservation(NetBoxModel):
     """