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<div class="titlepage"><div><div><h2 class="title">
<a name="tracker-examples-readonly"></a>Querying the Store</h2></div></div></div>
<p>
      In order to perform read-only queries to the store, a new
      <span class="type"><a class="link" href="TrackerSparqlConnection.html#TrackerSparqlConnection-struct" title="struct TrackerSparqlConnection">TrackerSparqlConnection</a></span>
      object must be acquired. In this case, as there is no intention of updating any
      value in the store, both the general connection (with
      <code class="function"><a class="link" href="TrackerSparqlConnection.html#tracker-sparql-connection-get" title="tracker_sparql_connection_get ()">tracker_sparql_connection_get</a></code>)
      or a specific direct-access connection (with
      <code class="function"><a class="link" href="TrackerSparqlConnection.html#tracker-sparql-connection-get-direct" title="tracker_sparql_connection_get_direct ()">tracker_sparql_connection_get_direct</a></code>)
      may be acquired. Note that in the latter case, every non read-only operation will result
      in an error being thrown by the TrackerSparqlConnection.
    </p>
<p>
      Once a proper connection object has been acquired, the read-only query can be launched either
      synchronously (<code class="function"><a class="link" href="TrackerSparqlConnection.html#tracker-sparql-connection-query" title="tracker_sparql_connection_query ()">tracker_sparql_connection_query</a></code>)
      or asynchronously (<code class="function"><a class="link" href="TrackerSparqlConnection.html#tracker-sparql-connection-query-async" title="tracker_sparql_connection_query_async ()">tracker_sparql_connection_query_async</a></code>).
      If launched asynchronously, the results of the query can be obtained with
      <code class="function"><a class="link" href="TrackerSparqlConnection.html#tracker-sparql-connection-query-finish" title="tracker_sparql_connection_query_finish ()">tracker_sparql_connection_query_finish</a></code>.
    </p>
<p>
      If the query was successful, a <span class="type"><a class="link" href="TrackerSparqlCursor.html#TrackerSparqlCursor-struct" title="struct TrackerSparqlCursor">TrackerSparqlCursor</a></span>
      will be available. You can now iterate the results of the query both synchronously (with
      <code class="function"><a class="link" href="TrackerSparqlCursor.html#tracker-sparql-cursor-next" title="tracker_sparql_cursor_next ()">tracker_sparql_cursor_next</a></code>) or
      asynchronously (with
      <code class="function"><a class="link" href="TrackerSparqlCursor.html#tracker-sparql-cursor-next-async" title="tracker_sparql_cursor_next_async ()">tracker_sparql_cursor_next_async</a></code> and
      <code class="function"><a class="link" href="TrackerSparqlCursor.html#tracker-sparql-cursor-next-finish" title="tracker_sparql_cursor_next_finish ()">tracker_sparql_cursor_next_finish</a></code>)
    </p>
<p>
      Once you end up with the query, remember to call <code class="function"><a href="/usr/share/gtk-doc/html/gobject/gobject-The-Base-Object-Type.html#g-object-unref">g_object_unref</a></code>
      for the <span class="type"><a class="link" href="TrackerSparqlCursor.html#TrackerSparqlCursor-struct" title="struct TrackerSparqlCursor">TrackerSparqlCursor</a></span>. And the same applies to the
      <span class="type"><a class="link" href="TrackerSparqlConnection.html#TrackerSparqlConnection-struct" title="struct TrackerSparqlConnection">TrackerSparqlConnection</a></span> when no longer needed.
    </p>
<p>
      The following program shows how Read-Only queries can be done to the store in a
      synchronous way:

</p>
<pre class="programlisting">
#include &lt;tracker-sparql.h&gt;

int main (int argc, const char **argv)
{
  GError *error = NULL;
  <span class="type"><a class="link" href="TrackerSparqlConnection.html#TrackerSparqlConnection-struct" title="struct TrackerSparqlConnection">TrackerSparqlConnection</a></span> *connection;
  <span class="type"><a class="link" href="TrackerSparqlCursor.html#TrackerSparqlCursor-struct" title="struct TrackerSparqlCursor">TrackerSparqlCursor</a></span> *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 = <code class="function"><a class="link" href="TrackerSparqlConnection.html#tracker-sparql-connection-get-direct" title="tracker_sparql_connection_get_direct ()">tracker_sparql_connection_get_direct</a></code> (NULL, &amp;error);
  if (!connection) {
    g_printerr ("Couldn't obtain a direct connection to the Tracker store: %s",
                error ? error-&gt;message : "unknown error");
    g_clear_error (&amp;error);

    return 1;
  }

  /* Make a synchronous query to the store */
  cursor = <code class="function"><a class="link" href="TrackerSparqlConnection.html#tracker-sparql-connection-query" title="tracker_sparql_connection_query ()">tracker_sparql_connection_query</a></code> (connection,
                                            query,
                                            NULL,
                                            &amp;error);

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

    return 1;
  }

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

    /* Iterate, synchronously, the results... */
    while (<code class="function"><a class="link" href="TrackerSparqlCursor.html#tracker-sparql-cursor-next" title="tracker_sparql_cursor_next ()">tracker_sparql_cursor_next</a></code> (cursor, NULL, &amp;error)) {
      g_print ("Result [%d]: %s\n",
	       i++,
	       <code class="function"><a class="link" href="TrackerSparqlCursor.html#tracker-sparql-cursor-get-string" title="tracker_sparql_cursor_get_string ()">tracker_sparql_cursor_get_string</a></code> (cursor, 0, NULL));
    }

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

    g_object_unref (cursor);
  }

  g_object_unref (connection);

  return 0;
}
</pre>
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libtracker-sparql-doc 0.16.2-1ubuntu4 / usr / share / gtk-doc / html / libtracker-sparql / tracker-examples-readonly.html
