Closes #4218: Allow negative voltage for DC power feeds

docs/release-notes/version-2.7.md

@@ -5,6 +5,7 @@
 ## Enhancements
 
 * [#3949](https://github.com/netbox-community/netbox/issues/3949) - Revised the installation docs and upgrade script to employ a Python virtual environment
+* [#4218](https://github.com/netbox-community/netbox/issues/4218) - Allow negative voltage for DC power feeds
 * [#4281](https://github.com/netbox-community/netbox/issues/4281) - Allow filtering device component list views by type
 * [#4284](https://github.com/netbox-community/netbox/issues/4284) - Add MRJ21 port and cable types
 * [#4290](https://github.com/netbox-community/netbox/issues/4290) - Include device name in tooltip on rack elevations

netbox/dcim/migrations/0099_powerfeed_negative_voltage.py

@@ -0,0 +1,19 @@
+# Generated by Django 2.2.10 on 2020-03-03 16:59
+
+from django.db import migrations, models
+import utilities.validators
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('dcim', '0098_devicetype_images'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='powerfeed',
+            name='voltage',
+            field=models.SmallIntegerField(default=120, validators=[utilities.validators.ExclusionValidator([0])]),
+        ),
+    ]

netbox/dcim/models/__init__.py

@@ -24,6 +24,7 @@ from extras.models import ConfigContextModel, CustomFieldModel, ObjectChange, Ta
 from utilities.fields import ColorField, NaturalOrderingField
 from utilities.models import ChangeLoggedModel
 from utilities.utils import serialize_object, to_meters
+from utilities.validators import ExclusionValidator
 from .device_component_templates import (
     ConsolePortTemplate, ConsoleServerPortTemplate, DeviceBayTemplate, FrontPortTemplate, InterfaceTemplate,
     PowerOutletTemplate, PowerPortTemplate, RearPortTemplate,
@@ -1775,9 +1776,9 @@ class PowerFeed(ChangeLoggedModel, CableTermination, CustomFieldModel):
         choices=PowerFeedPhaseChoices,
         default=PowerFeedPhaseChoices.PHASE_SINGLE
     )
-    voltage = models.PositiveSmallIntegerField(
+    voltage = models.SmallIntegerField(
-        validators=[MinValueValidator(1)],
+        default=POWERFEED_VOLTAGE_DEFAULT,
-        default=POWERFEED_VOLTAGE_DEFAULT
+        validators=[ExclusionValidator([0])]
     )
     amperage = models.PositiveSmallIntegerField(
         validators=[MinValueValidator(1)],
@@ -1859,10 +1860,16 @@ class PowerFeed(ChangeLoggedModel, CableTermination, CustomFieldModel):
                 self.rack, self.rack.site, self.power_panel, self.power_panel.site
             ))
 
+        # AC voltage cannot be negative
+        if self.voltage < 0 and self.supply == PowerFeedSupplyChoices.SUPPLY_AC:
+            raise ValidationError({
+                "voltage": "Voltage cannot be negative for AC supply"
+            })
+
     def save(self, *args, **kwargs):
 
         # Cache the available_power property on the instance
-        kva = self.voltage * self.amperage * (self.max_utilization / 100)
+        kva = abs(self.voltage) * self.amperage * (self.max_utilization / 100)
         if self.phase == PowerFeedPhaseChoices.PHASE_3PHASE:
             self.available_power = round(kva * 1.732)
         else:

netbox/utilities/validators.py

@@ -1,6 +1,6 @@
 import re
 
-from django.core.validators import _lazy_re_compile, URLValidator
+from django.core.validators import _lazy_re_compile, BaseValidator, URLValidator
 
 
 class EnhancedURLValidator(URLValidator):
@@ -26,3 +26,13 @@ class EnhancedURLValidator(URLValidator):
         r'(?:[/?#][^\s]*)?'                 # Path
         r'\Z', re.IGNORECASE)
     schemes = AnyURLScheme()
+
+
+class ExclusionValidator(BaseValidator):
+    """
+    Ensure that a field's value is not equal to any of the specified values.
+    """
+    message = 'This value may not be %(show_value)s.'
+
+    def compare(self, a, b):
+        return a in b