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/mixins.py

@@ -0,0 +1,45 @@
+from django.core.exceptions import ValidationError
+from django.db import models
+from dcim.choices import *
+from utilities.utils import to_grams
+
+
+class WeightMixin(models.Model):
+    weight = models.DecimalField(
+        max_digits=8,
+        decimal_places=2,
+        blank=True,
+        null=True
+    )
+    weight_unit = models.CharField(
+        max_length=50,
+        choices=WeightUnitChoices,
+        blank=True,
+    )
+    # Stores the normalized weight (in grams) for database ordering
+    _abs_weight = models.PositiveBigIntegerField(
+        blank=True,
+        null=True
+    )
+
+    class Meta:
+        abstract = True
+
+    def save(self, *args, **kwargs):
+
+        # Store the given weight (if any) in grams for use in database ordering
+        if self.weight and self.weight_unit:
+            self._abs_weight = to_grams(self.weight, self.weight_unit)
+        else:
+            self._abs_weight = None
+
+        super().save(*args, **kwargs)
+
+    def clean(self):
+        super().clean()
+
+        # Validate weight and weight_unit
+        if self.weight is not None and not self.weight_unit:
+            raise ValidationError("Must specify a unit when setting a weight")
+        elif self.weight is None:
+            self.weight_unit = ''