[grilo-plugins] tracker: Use standard Sparql1.1 syntax

[Carlos Garnacho <carlosg src gnome org>]

commit 8f80b1dcf749d2197aed89064465faf5a098813f
Author: Carlos Garnacho <carlosg gnome org>
Date:   Tue Aug 22 11:53:21 2017 +0200

    tracker: Use standard Sparql1.1 syntax
    
    The "AS var" syntax was non-standard, the Sparql1.1 spec defines this
    syntax as "AS ?var", which Tracker 1.x has also accepted for a very long
    time.
    
    Tracker 2.x is dropping the non-standard syntax, so switch the Tracker
    plugin to using the Sparql1.1 syntax, which shall work with Tracker 1.x
    and 2.x.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=786602

 src/tracker/grl-tracker-source-api.c |    6 +++---
 src/tracker/grl-tracker-utils.c      |    4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)
---
diff --git a/src/tracker/grl-tracker-source-api.c b/src/tracker/grl-tracker-source-api.c
index 31faabe..de4b185 100644
--- a/src/tracker/grl-tracker-source-api.c
+++ b/src/tracker/grl-tracker-source-api.c
@@ -763,9 +763,9 @@ grl_tracker_source_create_constraint (int min, int max)
  * <informalexample>
  *   <programlisting>
  *     SELECT rdf:type(?song)
- *            ?song            AS id
- *            nie:title(?song) AS title
- *            nie:url(?song)   AS url
+ *            ?song            AS ?id
+ *            nie:title(?song) AS ?title
+ *            nie:url(?song)   AS ?url
  *     WHERE { ?song a nmm:MusicPiece }
  *   </programlisting>
  * </informalexample>
diff --git a/src/tracker/grl-tracker-utils.c b/src/tracker/grl-tracker-utils.c
index e6e7c47..0984a3a 100644
--- a/src/tracker/grl-tracker-utils.c
+++ b/src/tracker/grl-tracker-utils.c
@@ -454,7 +454,7 @@ grl_tracker_source_get_select_string (const GList *keys)
 
   assoc_list = get_mapping_from_grl (grl_metadata_key_tracker_urn);
   assoc = (tracker_grl_sparql_t *) assoc_list->data;
-  g_string_append_printf (gstr, "%s AS %s ",
+  g_string_append_printf (gstr, "%s AS ?%s ",
                           assoc->sparql_key_attr_call,
                           assoc->sparql_key_name);
 
@@ -463,7 +463,7 @@ grl_tracker_source_get_select_string (const GList *keys)
     while (assoc_list != NULL) {
       assoc = (tracker_grl_sparql_t *) assoc_list->data;
       if (assoc != NULL) {
-        g_string_append_printf (gstr, "%s AS %s ",
+        g_string_append_printf (gstr, "%s AS ?%s ",
                                 assoc->sparql_key_attr_call,
                                 assoc->sparql_key_name);
       }