add get_by_metadata_key to AggregateList object

This change adds the get_by_metadata_key function to the AggregateList object
and the aggregate_get_by_metadata_key function to the DB API.

Previously, the only DB API function available for finding aggregates matching
a metadata key returned a dictionary of aggregated metadata. The
aggregate_get_by_metadata_key function returns all rows matching the specified
metadata key, and is called by the existing aggregate_host_get_by_metadata_key
DB API function.

The get_by_metadata_key function returns a list of Aggregate objects matching
the specified metadata key.

Related to blueprint compute-manager-objects-juno

Change-Id: If50c9f613dd192ab44577f26a81dd5b40e3a7af7

nova/objects/aggregate.py

@@ -151,7 +151,8 @@ class AggregateList(base.ObjectListBase, base.NovaObject):
     # Version 1.0: Initial version
     # Version 1.1: Added key argument to get_by_host()
     #              Aggregate <= version 1.1
-    VERSION = '1.1'
+    # Version 1.2: Added get_by_metadata_key
+    VERSION = '1.2'
 
     fields = {
         'objects': fields.ListOfObjectsField('Aggregate'),
@@ -160,8 +161,21 @@ class AggregateList(base.ObjectListBase, base.NovaObject):
         '1.0': '1.1',
         '1.1': '1.1',
         # NOTE(danms): Aggregate was at 1.1 before we added this
+        '1.2': '1.1',
         }
 
+    @classmethod
+    def _filter_db_aggregates(cls, db_aggregates, hosts):
+        if not isinstance(hosts, set):
+            hosts = set(hosts)
+        filtered_aggregates = []
+        for db_aggregate in db_aggregates:
+            for host in db_aggregate['hosts']:
+                if host in hosts:
+                    filtered_aggregates.append(db_aggregate)
+                    break
+        return filtered_aggregates
+
     @base.remotable_classmethod
     def get_all(cls, context):
         db_aggregates = db.aggregate_get_all(context)
@@ -173,3 +187,11 @@ class AggregateList(base.ObjectListBase, base.NovaObject):
         db_aggregates = db.aggregate_get_by_host(context, host, key=key)
         return base.obj_make_list(context, cls(context), objects.Aggregate,
                                   db_aggregates)
+
+    @base.remotable_classmethod
+    def get_by_metadata_key(cls, context, key, hosts=None):
+        db_aggregates = db.aggregate_get_by_metadata_key(context, key=key)
+        if hosts:
+            db_aggregates = cls._filter_db_aggregates(db_aggregates, hosts)
+        return base.obj_make_list(context, cls(context), objects.Aggregate,
+                                  db_aggregates)