Improve "objects.db.api.count" method

Two improvements are implemented in this method:
- Add a query limit number parameter. This parameter is used by
  "NeutronDbObject.objects_exist" to limit the number of registers
  retrieved to 1.
- Add a query field parameter. This is the name (string) of the
  "obj_cls.fields" list. That will reduce the columns to be
  retrieved to only one. To check the existence of a DB register,
  there is not need to retrieve the full DB model including the back
  references.
  In case of not passing any value, the first "obj_cls.primary_keys"
  value will be used instead.

Closes-Bug: #1925528

Change-Id: I9fd5e306e293102c366d89c01bbe8b13721d59b0

lower-constraints.txt

@@ -50,7 +50,7 @@ msgpack-python==0.4.0
 munch==2.1.0
 netaddr==0.7.18
 netifaces==0.10.4
-neutron-lib==2.10.1
+neutron-lib==2.11.0
 openstacksdk==0.31.2
 os-client-config==1.28.0
 os-ken==0.3.0

neutron/objects/base.py

@@ -933,5 +933,5 @@ class NeutronDbObject(NeutronObject, metaclass=DeclarativeObject):
             cls.validate_filters(**kwargs)
         # Succeed if at least a single object matches; no need to fetch more
         return bool(obj_db_api.count(
-            cls, context, **cls.modify_fields_to_db(kwargs))
+            cls, context, query_limit=1, **cls.modify_fields_to_db(kwargs))
         )

neutron/objects/db/api.py

@@ -20,11 +20,13 @@ from oslo_utils import uuidutils
 
 
 # Common database operation implementations
-def _get_filter_query(obj_cls, context, **kwargs):
+def _get_filter_query(obj_cls, context, query_field=None, query_limit=None,
+                      **kwargs):
     with obj_cls.db_context_reader(context):
         filters = _kwargs_to_filters(**kwargs)
         query = model_query.get_collection_query(
-            context, obj_cls.db_model, filters)
+            context, obj_cls.db_model, filters, limit=query_limit,
+            field=query_field)
         return query
 
 
@@ -32,8 +34,13 @@ def get_object(obj_cls, context, **kwargs):
     return _get_filter_query(obj_cls, context, **kwargs).first()
 
 
-def count(obj_cls, context, **kwargs):
+def count(obj_cls, context, query_field=None, query_limit=None, **kwargs):
-    return _get_filter_query(obj_cls, context, **kwargs).count()
+    if not query_field and obj_cls.primary_keys:
+        query_field = obj_cls.primary_keys[0]
+        if query_field in obj_cls.fields_need_translation:
+            query_field = obj_cls.fields_need_translation[query_field]
+    return _get_filter_query(obj_cls, context, query_field=query_field,
+                             query_limit=query_limit, **kwargs).count()
 
 
 def _kwargs_to_filters(**kwargs):

requirements.txt

@@ -16,7 +16,7 @@ Jinja2>=2.10 # BSD License (3 clause)
 keystonemiddleware>=5.1.0 # Apache-2.0
 netaddr>=0.7.18 # BSD
 netifaces>=0.10.4 # MIT
-neutron-lib>=2.10.1 # Apache-2.0
+neutron-lib>=2.11.0 # Apache-2.0
 python-neutronclient>=6.7.0 # Apache-2.0
 tenacity>=6.0.0 # Apache-2.0
 SQLAlchemy>=1.2.0 # MIT