[tracker] tracker-extract: Use safer method to insert tags in PNG module

[Carlos Garnacho <carlosg src gnome org>]

commit 493084b06137824c8cd1d6673a77d6a51cca5df0
Author: Carlos Garnacho <carlosg gnome org>
Date:   Mon Mar 14 12:46:05 2016 +0100

    tracker-extract: Use safer method to insert tags in PNG module
    
    The current way of inserting the nao:hasTag relationship on the
    extracted file involves one join operation per tag being inserted.
    This has performance implications, plus we can feasibly hit the
    sqlite limit of 64 tables in joins.
    
    Instead insert the tags in separate inserts, that will be as fast
    as it gets, plus there's no limit in the number of tags.

 src/tracker-extract/tracker-extract-png.c |   64 +++++++++++++----------------
 1 files changed, 29 insertions(+), 35 deletions(-)
---
diff --git a/src/tracker-extract/tracker-extract-png.c b/src/tracker-extract/tracker-extract-png.c
index 45d4836..a7aa705 100644
--- a/src/tracker-extract/tracker-extract-png.c
+++ b/src/tracker-extract/tracker-extract-png.c
@@ -185,12 +185,12 @@ raw_profile_new (const gchar *input,
 static void
 read_metadata (TrackerSparqlBuilder *preupdate,
                TrackerSparqlBuilder *metadata,
-               GString              *where,
                png_structp           png_ptr,
                png_infop             info_ptr,
                png_infop             end_ptr,
                const gchar          *uri,
-               const gchar          *graph)
+               const gchar          *graph,
+               const gchar          *urn)
 {
        MergeData md = { 0 };
        PngData pd = { 0 };
@@ -361,7 +361,7 @@ read_metadata (TrackerSparqlBuilder *preupdate,
        md.make = tracker_coalesce_strip (2, xd->make, ed->make);
        md.model = tracker_coalesce_strip (2, xd->model, ed->model);
 
-       keywords = g_ptr_array_new ();
+       keywords = g_ptr_array_new_with_free_func ((GDestroyNotify) g_free);
 
        if (md.comment) {
                tracker_sparql_builder_predicate (metadata, "nie:comment");
@@ -695,31 +695,21 @@ read_metadata (TrackerSparqlBuilder *preupdate,
        }
 
        for (i = 0; i < keywords->len; i++) {
-               gchar *p, *escaped, *var;
+               gchar *escaped, *subject;
+               const gchar *p;
 
                p = g_ptr_array_index (keywords, i);
                escaped = tracker_sparql_escape_string (p);
-               var = g_strdup_printf ("tag%d", i + 1);
+               subject = g_strdup_printf ("_:tag%d", i + 1);
 
                /* ensure tag with specified label exists */
-               tracker_sparql_builder_append (preupdate, "INSERT { ");
-
-               if (graph) {
-                       tracker_sparql_builder_append (preupdate, "GRAPH <");
-                       tracker_sparql_builder_append (preupdate, graph);
-                       tracker_sparql_builder_append (preupdate, "> { ");
-               }
-
-               tracker_sparql_builder_append (preupdate,
-                                              "_:tag a nao:Tag ; nao:prefLabel \"");
-               tracker_sparql_builder_append (preupdate, escaped);
-               tracker_sparql_builder_append (preupdate, "\"");
-
-               if (graph) {
-                       tracker_sparql_builder_append (preupdate, " } ");
-               }
-
-               tracker_sparql_builder_append (preupdate, " }\n");
+               tracker_sparql_builder_insert_open (preupdate, graph);
+               tracker_sparql_builder_subject (preupdate, subject);
+               tracker_sparql_builder_predicate (preupdate, "a");
+               tracker_sparql_builder_object (preupdate, "nao:Tag");
+               tracker_sparql_builder_predicate (preupdate, "nao:prefLabel");
+               tracker_sparql_builder_object_unvalidated (preupdate, escaped);
+               tracker_sparql_builder_insert_close (preupdate);
                tracker_sparql_builder_append (preupdate,
                                               "WHERE { FILTER (NOT EXISTS { "
                                               "?tag a nao:Tag ; nao:prefLabel \"");
@@ -728,14 +718,21 @@ read_metadata (TrackerSparqlBuilder *preupdate,
                                               "\" }) }\n");
 
                /* associate file with tag */
-               tracker_sparql_builder_predicate (metadata, "nao:hasTag");
-               tracker_sparql_builder_object_variable (metadata, var);
-
-               g_string_append_printf (where, "?%s a nao:Tag ; nao:prefLabel \"%s\" .\n", var, escaped);
+               tracker_sparql_builder_insert_open (preupdate, graph);
+               tracker_sparql_builder_subject_iri (preupdate, urn);
+               tracker_sparql_builder_predicate (preupdate, "nao:hasTag");
+               tracker_sparql_builder_object (preupdate, "?tag");
+               tracker_sparql_builder_insert_close (preupdate);
+               tracker_sparql_builder_where_open (preupdate);
+               tracker_sparql_builder_subject (preupdate, "?tag");
+               tracker_sparql_builder_predicate (preupdate, "a");
+               tracker_sparql_builder_object (preupdate, "nao:Tag");
+               tracker_sparql_builder_predicate (preupdate, "nao:prefLabel");
+               tracker_sparql_builder_object_unvalidated (preupdate, escaped);
+               tracker_sparql_builder_where_close (preupdate);
 
-               g_free (var);
+               g_free (subject);
                g_free (escaped);
-               g_free (p);
        }
        g_ptr_array_free (keywords, TRUE);
 
@@ -796,10 +793,9 @@ tracker_extract_get_metadata (TrackerExtractInfo *info)
        png_uint_32 width, height;
        gint bit_depth, color_type;
        gint interlace_type, compression_type, filter_type;
-       const gchar *dlna_profile, *dlna_mimetype, *graph;
+       const gchar *dlna_profile, *dlna_mimetype, *graph, *urn;
        TrackerSparqlBuilder *preupdate, *metadata;
        gchar *filename, *uri;
-       GString *where;
        GFile *file;
 
        file = tracker_extract_info_get_file (info);
@@ -809,6 +805,7 @@ tracker_extract_get_metadata (TrackerExtractInfo *info)
        preupdate = tracker_extract_info_get_preupdate_builder (info);
        metadata = tracker_extract_info_get_metadata_builder (info);
        graph = tracker_extract_info_get_graph (info);
+       urn = tracker_extract_info_get_urn (info);
 
        if (size < 64) {
                return FALSE;
@@ -892,11 +889,8 @@ tracker_extract_get_metadata (TrackerExtractInfo *info)
        tracker_sparql_builder_object (metadata, "nmm:Photo");
 
        uri = g_file_get_uri (file);
-       where = g_string_new ("");
 
-       read_metadata (preupdate, metadata, where, png_ptr, info_ptr, end_ptr, uri, graph);
-       tracker_extract_info_set_where_clause (info, where->str);
-       g_string_free (where, TRUE);
+       read_metadata (preupdate, metadata, png_ptr, info_ptr, end_ptr, uri, graph, urn);
        g_free (uri);
 
        tracker_sparql_builder_predicate (metadata, "nfo:width");