Explicitly compare IDs to None

Many database IDs (Resource, WatchRule) are integers, so 0 is a valid ID
and evaluating it in a boolean context may give the wrong result for the
first entry in the table. Even for the ones that aren't (e.g. Stack) it's
better to explicitly compare to None.

Change-Id: Id95eeb5cd0f9cac82937fae48122ce5fa90ca48d

heat/engine/resource.py

@@ -623,8 +623,8 @@ class Resource(status.ResourceStatus):
 
     def __str__(self):
         class_name = reflection.get_class_name(self, fully_qualified=False)
-        if self.stack.id:
-            if self.resource_id:
+        if self.stack.id is not None:
+            if self.resource_id is not None:
                 text = '%s "%s" [%s] %s' % (class_name, self.name,
                                             self.resource_id,
                                             six.text_type(self.stack))
@@ -2309,7 +2309,7 @@ class Resource(status.ResourceStatus):
 
         :returns: a dict representing the resource data for this resource.
         """
-        if self._data is None and self.id:
+        if self._data is None and self.id is not None:
             try:
                 self._data = resource_data_objects.ResourceData.get_all(self)
             except exception.NotFound:

heat/engine/stack.py

@@ -360,7 +360,7 @@ class Stack(collections.Mapping):
         return resources or None
 
     def db_resource_get(self, name):
-        if not self.id:
+        if self.id is None:
             return None
         return self._db_resources_get().get(name)
 
@@ -461,7 +461,7 @@ class Stack(collections.Mapping):
         Includes nested stacks below.
         """
         if not stack_id:
-            if not self.id:
+            if self.id is None:
                 # We're not stored yet, so we don't have anything to count
                 return 0
             stack_id = self.id
@@ -653,7 +653,7 @@ class Stack(collections.Mapping):
         else:
             s['raw_template_id'] = self.t.id
 
-        if self.id:
+        if self.id is not None:
             if exp_trvsl is None and not ignore_traversal_check:
                 exp_trvsl = self.current_traversal
 

heat/engine/watchrule.py

@@ -111,7 +111,7 @@ class WatchRule(object):
             'stack_id': self.stack_id
         }
 
-        if not self.id:
+        if self.id is None:
             wr = watch_rule_objects.WatchRule.create(self.context, wr_values)
             self.id = wr.id
         else:
@@ -120,7 +120,7 @@ class WatchRule(object):
 
     def destroy(self):
         """Delete the watchrule from the database."""
-        if self.id:
+        if self.id is not None:
             watch_rule_objects.WatchRule.delete(self.context, self.id)
 
     def do_data_cmp(self, data, threshold):