[tracker/async-queries] libtracker-db: Support empty result sets in async queries

[Jürg Billeter <juergbi src gnome org>]

commit 009551fab747faaa1ea4ca6768598dd120b8a8f8
Author: Jürg Billeter <j bitron ch>
Date:   Wed Apr 14 10:24:32 2010 +0200

    libtracker-db: Support empty result sets in async queries

 src/libtracker-db/tracker-db-manager.c |   21 +++++++++++++++------
 1 files changed, 15 insertions(+), 6 deletions(-)
---
diff --git a/src/libtracker-db/tracker-db-manager.c b/src/libtracker-db/tracker-db-manager.c
index 458bfa6..cccf6db 100644
--- a/src/libtracker-db/tracker-db-manager.c
+++ b/src/libtracker-db/tracker-db-manager.c
@@ -1366,15 +1366,18 @@ interface_pool_dispatch_cb (gpointer data,
 		g_simple_async_result_set_from_error (G_SIMPLE_ASYNC_RESULT (job->async_result), error);
 		g_error_free (error);
 	} else {
-		TrackerDBResultSet *result_set;
+		TrackerDBResultSet *result_set = NULL;
 		guint n_columns;
 
 		n_columns = tracker_db_cursor_get_n_columns (cursor);
-		result_set = _tracker_db_result_set_new (n_columns);
 
 		while (tracker_db_cursor_iter_next (cursor)) {
 			GValue val = { 0 };
 
+			if (G_UNLIKELY (!result_set)) {
+				result_set = _tracker_db_result_set_new (n_columns);
+			}
+
 			_tracker_db_result_set_append (result_set);
 
 			for (i = 0; i < n_columns; i++) {
@@ -1402,9 +1405,11 @@ interface_pool_dispatch_cb (gpointer data,
 		if (job->cancellable &&
 		    g_cancellable_set_error_if_cancelled (job->cancellable, &error)) {
 			g_simple_async_result_set_from_error (G_SIMPLE_ASYNC_RESULT (job->async_result), error);
-			g_object_unref (result_set);
+			if (result_set) {
+				g_object_unref (result_set);
+			}
 			g_error_free (error);
-		} else {
+		} else if (result_set) {
 			g_simple_async_result_set_op_res_gpointer (G_SIMPLE_ASYNC_RESULT (job->async_result),
 			                                           result_set, (GDestroyNotify) g_object_unref);
 		}
@@ -1459,9 +1464,13 @@ tracker_db_interface_pool_execute_query_finish (TrackerDBInterfacePool	*pool,
 		return NULL;
 	}
 
-	result_set = TRACKER_DB_RESULT_SET (g_simple_async_result_get_op_res_gpointer (result));
+	result_set = g_simple_async_result_get_op_res_gpointer (result);
 
-	return g_object_ref (result_set);
+	if (result_set) {
+		return g_object_ref (result_set);
+	} else {
+		return NULL;
+	}
 }
 
 void