为可空类型提供类库支持，包括转换运算符和算术运算符。

Library Support for nullable types, including conversion operators and arithmetic operators.

youdao

可置空类型和 空合并运算符

Nullable types and null coalescing operator

youdao

如果数据库中的一列被标志为可空，那么数据模型类相应的属性将是一个可空的类型。

If a column in the database is marked as being nullable, then the corresponding property in the data model class created by the LINQ to SQL designer will be a nullable type.

youdao