Lazy-load stack tags

Tags for a stack need to be loaded in the following scenarios:
- To display during a stack show
- To store during a create or update

All other operations which require a loaded stack will likely not
reference the tags, so the extra SQL query which always loads them is
often not necessary.

This change removes the tags loading from stack_object.Stack and
stack.Stack.load and implements annotated properties functions for a
Stack.tags property so that they are loaded from the database on
command.

Change-Id: Iecbf4f101b7f264a42b57f720a8428b0aed706e2
Partial-Bug: #1578851

heat/engine/stack.py

@@ -172,6 +172,7 @@ class Stack(collections.Mapping):
         self._dependencies = None
         self._access_allowed_handlers = {}
         self._db_resources = None
+        self._tags = tags
         self.adopt_stack_data = adopt_stack_data
         self.stack_user_project_id = stack_user_project_id
         self.created_time = created_time
@@ -230,6 +231,19 @@ class Stack(collections.Mapping):
         else:
             self.outputs = {}
 
+    @property
+    def tags(self):
+        if self._tags is None:
+            tags = stack_tag_object.StackTagList.get(
+                self.context, self.id)
+            if tags:
+                self._tags = [t.tag for t in tags]
+        return self._tags
+
+    @tags.setter
+    def tags(self, value):
+        self._tags = value
+
     @property
     def worker_client(self):
         """Return a client for making engine RPC calls."""
@@ -494,9 +508,6 @@ class Stack(collections.Mapping):
                  use_stored_context=False, cache_data=None):
         template = tmpl.Template.load(
             context, stack.raw_template_id, stack.raw_template)
-        tags = None
-        if stack.tags:
-            tags = [t.tag for t in stack.tags]
         return cls(context, stack.name, template,
                    stack_id=stack.id,
                    action=stack.action, status=stack.status,
@@ -512,7 +523,7 @@ class Stack(collections.Mapping):
                    user_creds_id=stack.user_creds_id, tenant_id=stack.tenant,
                    use_stored_context=use_stored_context,
                    username=stack.username, convergence=stack.convergence,
-                   current_traversal=stack.current_traversal, tags=tags,
+                   current_traversal=stack.current_traversal,
                    prev_raw_template_id=stack.prev_raw_template_id,
                    current_deps=stack.current_deps, cache_data=cache_data)
 

heat/objects/stack.py

@@ -60,7 +60,6 @@ class Stack(
         'current_deps': heat_fields.JsonField(),
         'prev_raw_template_id': fields.IntegerField(),
         'prev_raw_template': fields.ObjectField('RawTemplate'),
-        'tags': fields.ObjectField('StackTagList'),
         'parent_resource_name': fields.StringField(nullable=True),
     }
 
@@ -71,9 +70,6 @@ class Stack(
                 stack['raw_template'] = (
                     raw_template.RawTemplate.get_by_id(
                         context, db_stack['raw_template_id']))
-            elif field == 'tags':
-                stack['tags'] = stack_tag.StackTagList.from_db_object(
-                    context, db_stack.get(field))
             else:
                 stack[field] = db_stack.__dict__.get(field)
         stack._context = context
@@ -215,3 +211,7 @@ class Stack(
     def identifier(self):
         """Return an identifier for this stack."""
         return identifier.HeatIdentifier(self.tenant, self.name, self.id)
+
+    @property
+    def tags(self):
+        return stack_tag.StackTagList.get(self._context, self.id)

heat/tests/test_stack.py

@@ -347,7 +347,6 @@ class StackTest(common.HeatTestCase):
                              username=mox.IgnoreArg(),
                              convergence=False,
                              current_traversal=self.stack.current_traversal,
-                             tags=mox.IgnoreArg(),
                              prev_raw_template_id=None,
                              current_deps=None, cache_data=None)
 
@@ -1276,6 +1275,23 @@ class StackTest(common.HeatTestCase):
         ctx_expected['auth_token'] = None
         self.assertEqual(ctx_expected, self.stack.stored_context().to_dict())
 
+    def test_tags_property_get_set(self):
+        self.stack = stack.Stack(self.ctx, 'stack_tags', self.tmpl)
+        self.stack.store()
+        stack_id = self.stack.id
+        test_stack = stack.Stack.load(self.ctx, stack_id=stack_id)
+        self.assertIsNone(test_stack.tags)
+
+        self.stack = stack.Stack(self.ctx, 'stack_name', self.tmpl)
+        self.stack.tags = ['tag1', 'tag2']
+        self.assertEqual(['tag1', 'tag2'], self.stack._tags)
+        self.stack.store()
+        stack_id = self.stack.id
+        test_stack = stack.Stack.load(self.ctx, stack_id=stack_id)
+        self.assertIsNone(test_stack._tags)
+        self.assertEqual(['tag1', 'tag2'], test_stack.tags)
+        self.assertEqual(['tag1', 'tag2'], test_stack._tags)
+
     def test_load_reads_tags(self):
         self.stack = stack.Stack(self.ctx, 'stack_tags', self.tmpl)
         self.stack.store()