Add selection for vpnnetworkreservations

uncloud_net/selectors.py

@@ -0,0 +1,23 @@
+from django.db.models import Count
+from .models import *
+
+@transaction.atomic
+def get_suitable_pool(subnetwork_size):
+    """
+    Find suitable pools for a certain network size.
+
+    First, filter for all pools that offer the requested subnetwork_size.
+
+    Then find those pools that are not fully exhausted:
+
+    The number of available networks in a pool is 2^(subnetwork_size-network_size.
+
+    The number of available networks in a pool is given by the number of VPNNetworkreservations.
+
+    """
+
+    return VPNPool.objects.annotate(
+        num_reservations=Count('vpnnetworkreservation'),
+        max_reservations=2**(F('subnetwork_size')-F('network_size'))).filter(
+            num_reservations__lt=F('max_reservations'),
+            subnetwork_size=subnetwork_size)