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

[Carlos Garnacho <carlosg src gnome org>]

commit 38bdc9d9e91273802ebb95111ed7ca745b66c537
Author: Carlos Garnacho <carlosg gnome org>
Date:   Mon Mar 14 02:51:08 2016 +0100

    tracker-extract: Use safer method to insert tags in PDF 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-pdf.c |   61 +++++++++++++----------------
 1 files changed, 27 insertions(+), 34 deletions(-)
---
diff --git a/src/tracker-extract/tracker-extract-pdf.c b/src/tracker-extract/tracker-extract-pdf.c
index b750678..6402ddd 100644
--- a/src/tracker-extract/tracker-extract-pdf.c
+++ b/src/tracker-extract/tracker-extract-pdf.c
@@ -298,6 +298,7 @@ tracker_extract_get_metadata (TrackerExtractInfo *info)
        GError *error = NULL;
        TrackerSparqlBuilder *metadata, *preupdate;
        const gchar *graph;
+       const gchar *urn;
        TrackerXmpData *xd = NULL;
        PDFData pd = { 0 }; /* actual data */
        PDFData md = { 0 }; /* for merging */
@@ -306,7 +307,6 @@ tracker_extract_get_metadata (TrackerExtractInfo *info)
        gchar *content, *uri;
        guint n_bytes;
        GPtrArray *keywords;
-       GString *where;
        guint i;
        GFile *file;
        gchar *filename;
@@ -318,6 +318,7 @@ tracker_extract_get_metadata (TrackerExtractInfo *info)
        metadata = tracker_extract_info_get_metadata_builder (info);
        preupdate = tracker_extract_info_get_preupdate_builder (info);
        graph = tracker_extract_info_get_graph (info);
+       urn = tracker_extract_info_get_urn (info);
 
        file = tracker_extract_info_get_file (info);
        filename = g_file_get_path (file);
@@ -413,7 +414,7 @@ tracker_extract_get_metadata (TrackerExtractInfo *info)
                pd.creation_date = tracker_date_to_string ((time_t) creation_date);
        }
 
-       keywords = g_ptr_array_new ();
+       keywords = g_ptr_array_new_with_free_func ((GDestroyNotify) g_free);
 
        if (xml && *xml &&
            (xd = tracker_xmp_new (xml, strlen (xml), uri)) != NULL) {
@@ -680,34 +681,22 @@ tracker_extract_get_metadata (TrackerExtractInfo *info)
                write_pdf_data (pd, metadata, keywords);
        }
 
-       where = g_string_new ("");
-
        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 \"");
@@ -716,20 +705,24 @@ tracker_extract_get_metadata (TrackerExtractInfo *info)
                                               "\" }) }\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);
-
-               g_free (var);
+               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 (subject);
                g_free (escaped);
-               g_free (p);
        }
        g_ptr_array_free (keywords, TRUE);
 
-       tracker_extract_info_set_where_clause (info, where->str);
-       g_string_free (where, TRUE);
-
        tracker_sparql_builder_predicate (metadata, "nfo:pageCount");
        tracker_sparql_builder_object_int64 (metadata, poppler_document_get_n_pages (document));