An IO optimised method for accessing resource data

This provides a wrapper over the db_api.resource_data_* methods that
attempts to avoid unnecessary database calls for get operations.

On resource create, all resource data is loaded with a single query and
stored with the resource as a dict. Calling data_set() or data_delete()
clears this dict so the next time data() is called all resource
data is loaded again from the database.

There is a future potential optimisation to prefetch the resource.data on
resource_get_by_name_and_stack, which would result in zero resource data
queries for a Stack.load.

This is part of an effort to reduce the number of database queries required
for a Stack.load operation.

Change-Id: I2564a9f953841d895acd5b853a67aa4bc375b635
Related-Bug: #1306743

heat/engine/resource.py

@@ -163,7 +163,10 @@ class Resource(object):
             self.status = resource.status
             self.status_reason = resource.status_reason
             self.id = resource.id
-            self.data = resource.data
+            try:
+                self._data = db_api.resource_data_get_all(self, resource.data)
+            except exception.NotFound:
+                self._data = {}
             self.created_time = resource.created_at
             self.updated_time = resource.updated_at
         else:
@@ -176,7 +179,7 @@ class Resource(object):
             self.status = self.COMPLETE
             self.status_reason = ''
             self.id = None
-            self.data = []
+            self._data = {}
             self.created_time = None
             self.updated_time = None
 
@@ -486,7 +489,7 @@ class Resource(object):
         # save the resource data
         if data and isinstance(data, dict):
             for key, value in data.iteritems():
-                db_api.resource_data_set(self, key, value)
+                self.data_set(key, value)
 
         # save the resource metadata
         self.metadata = metadata
@@ -929,3 +932,41 @@ class Resource(object):
             },
             'Outputs': Attributes.as_outputs(resource_name, cls)
         }
+
+    def data(self):
+        '''
+        Resource data for this resource
+
+        Use methods data_set and data_delete to modify the resource data
+        for this resource.
+
+        :returns: a dict representing the resource data for this resource.
+        '''
+        if self._data is None and self.id:
+            try:
+                self._data = db_api.resource_data_get_all(self)
+            except exception.NotFound:
+                pass
+
+        return self._data or {}
+
+    def data_set(self, key, value, redact=False):
+        '''Save resource's key/value pair to database.'''
+        db_api.resource_data_set(self, key, value, redact)
+        # force fetch all resource data from the database again
+        self._data = None
+
+    def data_delete(self, key):
+        '''
+        Remove a resource_data element associated to a resource.
+
+        :returns: True if the key existed to delete
+        '''
+        try:
+            db_api.resource_data_delete(self, key)
+        except exception.NotFound:
+            return False
+        else:
+            # force fetch all resource data from the database again
+            self._data = None
+            return True

heat/tests/test_nested_stack.py

@@ -639,7 +639,7 @@ Resources:
 
 class ResDataResource(generic_rsrc.GenericResource):
     def handle_create(self):
-        db_api.resource_data_set(self, "test", 'A secret value', True)
+        self.data_set("test", 'A secret value', True)
 
 
 class ResDataNestedStackTest(NestedStackTest):

heat/tests/test_sqlalchemy_api.py

@@ -82,7 +82,7 @@ class MyResource(Resource):
 
     @my_secret.setter
     def my_secret(self, my_secret):
-        db_api.resource_data_set(self, 'my_secret', my_secret, True)
+        self.data_set('my_secret', my_secret, True)
 
 
 class SqlAlchemyTest(HeatTestCase):
@@ -275,7 +275,7 @@ class SqlAlchemyTest(HeatTestCase):
         self.m.ReplayAll()
         stack.create()
         rsrc = stack['WebServer']
-        db_api.resource_data_set(rsrc, 'test', 'test_data')
+        rsrc.data_set('test', 'test_data')
         self.assertEqual('test_data', db_api.resource_data_get(rsrc, 'test'))
         db_api.resource_data_delete(rsrc, 'test')
         self.assertRaises(exception.NotFound,