Add some bulk lookup methods to ML2 for RPC handling

This adds three methods to make working with bulk port
DB lookups easier in ML2:

* partial_port_ids_to_full_ids: takes short port IDs map to
  full port IDs. This will allow us to eliminate many LIKE
  queries and do one just once for all ports on an RPC call.
* get_port_db_objects: Takes a list of port IDs and returns
  a map to port DB objects. This allows us to get access to
  sqla obejcts for a bunch of ports without a custom
  session.query call.
* get_network_contexts: Takes a list of network_ids and does
  a bulk construction of NetworkContext objects and returns
  them as a map of network_id to NetworkContext to avoid
  expensive net lookups when constructing lots of PortContext
  objects.

Partial-Bug: #1665215
Change-Id: I330eefbf429bd62f2a7e8ebadf7037da15c86815

neutron/plugins/ml2/db.py

@@ -292,6 +292,46 @@ def get_distributed_port_bindings(context, port_id):
     return bindings
 
 
+@db_api.context_manager.reader
+def partial_port_ids_to_full_ids(context, partial_ids):
+    """Takes a list of the start of port IDs and returns full IDs.
+
+    Returns dictionary of partial IDs to full IDs if a single match
+    is found.
+    """
+    result = {}
+    to_full_query = (context.session.query(models_v2.Port.id).
+                     filter(or_(*[models_v2.Port.id.startswith(p)
+                                  for p in partial_ids])))
+    candidates = [match[0] for match in to_full_query]
+    for partial_id in partial_ids:
+        matching = [c for c in candidates if c.startswith(partial_id)]
+        if len(matching) == 1:
+            result[partial_id] = matching[0]
+            continue
+        if len(matching) < 1:
+            LOG.info("No ports have port_id starting with %s", partial_id)
+        elif len(matching) > 1:
+            LOG.error(_LE("Multiple ports have port_id starting with %s"),
+                      partial_id)
+    return result
+
+
+@db_api.context_manager.reader
+def get_port_db_objects(context, port_ids):
+    """Takes a list of port_ids and returns matching port db objects.
+
+    return format is a dictionary keyed by passed in IDs with db objects
+    for values or None if the port was not present.
+    """
+    port_qry = (context.session.query(models_v2.Port).
+                filter(models_v2.Port.id.in_(port_ids)))
+    result = {p: None for p in port_ids}
+    for port in port_qry:
+        result[port.id] = port
+    return result
+
+
 @db_api.context_manager.reader
 def is_dhcp_active_on_any_subnet(context, subnet_ids):
     if not subnet_ids:

neutron/plugins/ml2/plugin.py

@@ -884,6 +884,23 @@ class Ml2Plugin(db_base_plugin_v2.NeutronDbPluginV2,
 
         return [db_utils.resource_fields(net, fields) for net in nets]
 
+    def get_network_contexts(self, context, network_ids):
+        """Return a map of network_id to NetworkContext for network_ids."""
+        net_filters = {'id': list(set(network_ids))}
+        nets_by_netid = {
+            n['id']: n for n in self.get_networks(context,
+                                                  filters=net_filters)
+        }
+        segments_by_netid = segments_db.get_networks_segments(
+            context, nets_by_netid.keys())
+        netctxs_by_netid = {
+            net_id: driver_context.NetworkContext(
+                self, context, nets_by_netid[net_id],
+                segments=segments_by_netid[net_id])
+            for net_id in nets_by_netid.keys()
+        }
+        return netctxs_by_netid
+
     @utils.transaction_guard
     def delete_network(self, context, id):
         # the only purpose of this override is to protect this from being