Closes #20564: Many-to-many pass-through port mappings (#20851)

netbox/dcim/models/base.py

@@ -0,0 +1,61 @@
+from django.core.exceptions import ValidationError
+from django.core.validators import MaxValueValidator, MinValueValidator
+from django.db import models
+from django.utils.translation import gettext_lazy as _
+
+from dcim.constants import PORT_POSITION_MAX, PORT_POSITION_MIN
+
+__all__ = (
+    'PortMappingBase',
+)
+
+
+class PortMappingBase(models.Model):
+    """
+    Base class for PortMapping and PortTemplateMapping
+    """
+    front_port_position = models.PositiveSmallIntegerField(
+        default=1,
+        validators=(
+            MinValueValidator(PORT_POSITION_MIN),
+            MaxValueValidator(PORT_POSITION_MAX),
+        ),
+    )
+    rear_port_position = models.PositiveSmallIntegerField(
+        default=1,
+        validators=(
+            MinValueValidator(PORT_POSITION_MIN),
+            MaxValueValidator(PORT_POSITION_MAX),
+        ),
+    )
+
+    _netbox_private = True
+
+    class Meta:
+        abstract = True
+        constraints = (
+            models.UniqueConstraint(
+                fields=('front_port', 'front_port_position'),
+                name='%(app_label)s_%(class)s_unique_front_port_position'
+            ),
+            models.UniqueConstraint(
+                fields=('rear_port', 'rear_port_position'),
+                name='%(app_label)s_%(class)s_unique_rear_port_position'
+            ),
+        )
+
+    def clean(self):
+        super().clean()
+
+        # Validate rear port position
+        if self.rear_port_position > self.rear_port.positions:
+            raise ValidationError({
+                "rear_port_position": _(
+                    "Invalid rear port position ({rear_port_position}): Rear port {name} has only {positions} "
+                    "positions."
+                ).format(
+                    rear_port_position=self.rear_port_position,
+                    name=self.rear_port.name,
+                    positions=self.rear_port.positions
+                )
+            })