因为SQLObject总是需要该字段对象，所以它总会创建一个。

Because SQLObject always needs this field object, it always creates one.

youdao

最后注意，无需在PhoneNumber中为id字段创建字段对象。

Finally, note that there's no need to create a field object in PhoneNumber for the id field.

youdao

定义操作字段与中间对象之间的映射。

Define the mapping between action fields and intermediate objects.

youdao