code: public boolean update() {
  		filter(FILTER_BY_UPDATE);
  		
  		if (_getModifyFlag().isEmpty()) {
  			return false;
  		}
  		
  		Table table = _getTable();
  		String[] pKeys = table.getPrimaryKey();
  		for (String pKey : pKeys) {
  			Object id = attrs.get(pKey);
  			if (id == null)
  				throw new ActiveRecordException("You can't update model without Primary Key, " + pKey + " can not be null.");
  		}
  		
  		Config config = _getConfig();
  		StringBuilder sql = new StringBuilder();
  		List<Object> paras = new ArrayList<Object>();
  		config.dialect.forModelUpdate(table, attrs, _getModifyFlag(), sql, paras);
  		
  		if (paras.size() <= 1) {	// Needn't update
  			return false;
  		}
  		
  		// --------
  		Connection conn = null;
  		try {
  			conn = config.getConnection();
  			int result = Db.update(config, conn, sql.toString(), paras.toArray());
  			if (result >= 1) {
  				_getModifyFlag().clear();
  				return true;
  			}
  			return false;
  		} catch (Exception e) {
  			throw new ActiveRecordException(e);
  		} finally {
  			config.close(conn);
  		}
  	}
docs: Update model.