C#无法隐式转换类型'int?' 'int' [英] C# Cannot implicitly convert type 'int?' to 'int'

问题描述

我有这个查询:

int cid =  (from c in dc.Cs
                where c.id == cid
                select c.clientid).FirstOrDefault();

return cid;

其中c.clientid可为空.但我收到此错误:

where c.clientid is nullable. But I receive this error:

无法隐式转换类型'int?'到"int".存在显式转换(您是否缺少演员表?)

Cannot implicitly convert type 'int?' to 'int'. An explicit conversion exists (are you missing a cast?)

推荐答案

好吧，int? 可以设为null，而int 不能.这就是编译器 complains 的原因:当查询返回null时，应将其分配给cid的原因.如果是null，您可以尝试提供一些默认值:

Well, int? can be null while int can't. That's why the compiler complains: what should it assign to cid when the query returns null. You can try providing some default value in case of null:

int cid = (  from c in dc.Cs
            where c.id == cid
           select c.clientid)
  .FirstOrDefault() ?? 0; //TODO: put the right default value instead of 0

return cid;

表示在null情况下返回0(请注意，您有两个可能性:1.第一项c.clientid为null； 2. dc.Cs当过滤后为空)，否则为int?.Value

which means return 0 in case of null (please, notice that you have two possibilities: 1. 1st item c.clientid is null; 2. dc.Cs when filtered is empty) and int?.Value otherwise

这篇关于C#无法隐式转换类型'int?' 'int'的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！