Question

var q = from p in query
where 
   ((criterias.birthday == p.BirthDay|| criterias.birthday == null))                                
&& ((criterias.marriageDate == null || criterias.marriageDate == p.MarriageDate))                                
&& ((criterias.gender == p.Gender) || (criterias.gender == null))
&& ((criterias.nationalities.Contains(p.Nationality)) || (criterias.nationalities == null))

标准是我存储搜索标准的类。民族是一个字符串列表。当我在字符串中没有项目时，会出现问题。查询抛出null引用异常。查询不接受国籍中的空值。我怎样才能解决这个问题？

Answer 1

反转顺序，以便在查询之前进行空检查：当您使用||时，表达式的第二部分仅在第一部分求值为false时进行评估：

&& ((criterias.nationalities == null) || 
             (criterias.nationalities.Contains(p.Nationality)))

Answer 2

看看这两个：

   ((criterias.birthday == p.BirthDay|| criterias.birthday == null))
&& ((criterias.marriageDate == null || criterias.marriageDate == p.MarriageDate))

我不认为weddingDate会给你带来问题，但生日会使用错误的订单在这种情况下，您需要||的“短路评估”属性，将其更改为：

   (criterias.birthday == null || criterias.birthday == p.BirthDay)
&& (criterias.marriageDate == null || criterias.marriageDate == p.MarriageDate)

Answer 3

尝试交换国税支票的顺序。在尝试评估Contains之前，它应该在空检查上短路。

((criterias.nationalities == null) || (criterias.nationalities.Contains(p.Nationality)))

Answer 4

转过这句话：

(criterias.nationalities.Contains(p.Nationality)) || (criterias.nationalities == null)

所以它读取

(criterias.nationalities == null) || (criterias.nationalities.Contains(p.Nationality))

如果第一个操作数的计算结果为true，则跳过第二个操作数。

Answer 5

首先尝试检查null然后（如果它不为null）检查包含：

var q = from p in query 
where     
((criterias.birthday == p.BirthDay|| criterias.birthday == null))                                 
&& ((criterias.marriageDate == null ||  criterias.marriageDate == p.MarriageDate))
&& ((criterias.gender == p.Gender) || (criterias.gender == null)) 
&& ((criterias.nationalities == null) || (criterias.nationalities.Contains(p.Nationality))

LINQ List在子句中给出了null异常

5 个答案: