code: public boolean update(String tableName, String primaryKey, Record record) {
  		Connection conn = null;
  		try {
  			conn = config.getConnection();
  			return update(config, conn, tableName, primaryKey, record);
  		} catch (Exception e) {
  			throw new ActiveRecordException(e);
  		} finally {
  			config.close(conn);
  		}
  	}
docs: Update Record.
  <pre>
  Example:
  Db.use().update("user_role", "user_id, role_id", record);
  </pre>
  @param tableName the table name of the Record save to
  @param primaryKey the primary key of the table, composite primary key is separated by comma character: ","
  @param record the Record object
  @param true if update succeed otherwise false