LINQ to SQL 和空字符串，我如何使用包含?

作者: 嗫?暁雲?
来源: 51数据库
2022-12-08

问题描述

这里是查询

from a in this._addresses
where a.Street.Contains(street) || a.StreetAdditional.Contains(streetAdditional)
select a).ToList<Address>()

如果 where 子句中的两个属性都有值，这可以正常工作，但例如，如果 a.StreetAdditional 为空(大多数情况下)，我将收到空引用异常.

if both properties in the where clause have values this works fine, but if for example, a.StreetAdditional is null (Most of the times), I will get a null reference exception.

有办法解决这个问题吗?

Is there a work around this?

谢谢，

推荐答案

最明显的一个:

from a in this._addresses
where (a.Street != null && a.Street.Contains(street)) || (a.StreetAdditional != null && a.StreetAdditional.Contains(streetAdditional))
select a).ToList<Address>()

或者，您可以为 Contains 编写一个扩展方法，该方法接受空参数而不会出错.有人可能会说，有这样的方法不是很好，因为它看起来像一个普通的方法调用，但允许有空值(从而搁置正常的空检查实践).

Alternatively you could write an extension method for Contains that accepts a null argument without error. Some might say that it is not so pretty to have such a method, because it looks like a normal method call, but is allowed for null values (thereby setting aside normal null-checking practices).

推荐阅读