function castInts() {
		foreach (static::$_columns as $column_name => &$type) {
			if ($this->{$column_name} === null || !static::isIntegerType($type)) {
				continue;
			}
			if ('' === $this->{$column_name}) {
				$this->{$column_name} = null;
				continue;
			}
			$this->{$column_name} = (int) $this->{$column_name};
		}
		return $this;
	}