Rack reservations (#900)

* Initial work on rack reservations

* Added views for rack reservations

* Implemented ArrayFieldSelectMultiple form widget

* Implemented API endpoints for rack reservations

* Tweaked the database migration

netbox/dcim/models.py

@@ -1,8 +1,10 @@
 from collections import OrderedDict
 
 from django.conf import settings
+from django.contrib.auth.models import User
 from django.contrib.contenttypes.models import ContentType
 from django.contrib.contenttypes.fields import GenericRelation
+from django.contrib.postgres.fields import ArrayField
 from django.core.exceptions import ValidationError
 from django.core.urlresolvers import reverse
 from django.core.validators import MaxValueValidator, MinValueValidator
@@ -478,6 +480,50 @@ class Rack(CreatedUpdatedModel, CustomFieldModel):
         return int(float(self.u_height - u_available) / self.u_height * 100)
 
 
+@python_2_unicode_compatible
+class RackReservation(models.Model):
+    """
+    One or more reserved units within a Rack.
+    """
+    rack = models.ForeignKey('Rack', related_name='reservations', editable=False, on_delete=models.CASCADE)
+    units = ArrayField(models.PositiveSmallIntegerField())
+    created = models.DateTimeField(auto_now_add=True)
+    user = models.ForeignKey(User, editable=False, on_delete=models.PROTECT)
+    description = models.CharField(max_length=100)
+
+    class Meta:
+        ordering = ['created']
+
+    def __str__(self):
+        return u"Reservation for rack {}".format(self.rack)
+
+    def clean(self):
+
+        if self.units:
+
+            # Validate that all specified units exist in the Rack.
+            invalid_units = [u for u in self.units if u not in self.rack.units]
+            if invalid_units:
+                raise ValidationError({
+                    'units': u"Invalid unit(s) for {}U rack: {}".format(
+                        self.rack.u_height,
+                        ', '.join([str(u) for u in invalid_units]),
+                    ),
+                })
+
+            # Check that none of the units has already been reserved for this Rack.
+            reserved_units = []
+            for resv in self.rack.reservations.exclude(pk=self.pk):
+                reserved_units += resv.units
+            conflicting_units = [u for u in self.units if u in reserved_units]
+            if conflicting_units:
+                raise ValidationError({
+                    'units': 'The following units have already been reserved: {}'.format(
+                        ', '.join([str(u) for u in conflicting_units]),
+                    )
+                })
+
+
 #
 # Device Types
 #