In order to perform read-only queries to the store, a new TrackerSparqlConnection object must be acquired. In this case, as there is no intention of updating any value in the store, both the general connection (with tracker_sparql_connection_get) or a specific direct-access connection (with tracker_sparql_connection_get_direct) may be acquired. Note that in the latter case, every non read-only operation will result in an error being thrown by the TrackerSparqlConnection.

Once a proper connection object has been acquired, the read-only query can be launched either synchronously (tracker_sparql_connection_query) or asynchronously (tracker_sparql_connection_query_async). If launched asynchronously, the results of the query can be obtained with tracker_sparql_connection_query_finish.

If the query was successful, a TrackerSparqlCursor will be available. You can now iterate the results of the query both synchronously (with tracker_sparql_cursor_next) or asynchronously (with tracker_sparql_cursor_next_async and tracker_sparql_cursor_next_finish)

Once you end up with the query, remember to call g_object_unref for the TrackerSparqlCursor. And the same applies to the TrackerSparqlConnection when no longer needed.

The following program shows how Read-Only queries can be done to the store in a synchronous way:

#include <tracker-sparql.h>

int main (int argc, const char **argv)
{
  GError *error = NULL;
  TrackerSparqlConnection *connection;
  TrackerSparqlCursor *cursor;
  const gchar *query = "SELECT nie:url(?u) WHERE { ?u a nfo:FileDataObject }";

  /* As we know only read-only queries will be done, it's enough
   * to use a connection with only direct-access setup. The NULL
   * represents a possible GCancellable.
   */
  connection = tracker_sparql_connection_get_direct (NULL, &error);
  if (!connection) {
    g_printerr ("Couldn't obtain a direct connection to the Tracker store: %s",
                error ? error->message : "unknown error");
    g_clear_error (&error);

    return 1;
  }

  /* Make a synchronous query to the store */
  cursor = tracker_sparql_connection_query (connection,
                                            query,
                                            NULL,
                                            &error);

  if (error) {
    /* Some error happened performing the query, not good */
    g_printerr ("Couldn't query the Tracker Store: '%s'",
                error ? error->message : "unknown error");
    g_clear_error (&error);

    return 1;
  }

  /* Check results... */
  if (!cursor) {
    g_print ("No results found :-/\n");
  } else {
    gint i = 0;

    /* Iterate, synchronously, the results... */
    while (tracker_sparql_cursor_next (cursor, NULL, &error)) {
      g_print ("Result [%d]: %s\n",
	       i++,
	       tracker_sparql_cursor_get_string (cursor, 0, NULL));
    }

    g_print ("A total of '%d' results were found\n", i);

    g_object_unref (cursor);
  }

  g_object_unref (connection);

  return 0;
}