LINQ错误：null值不能分配给类型System.Int32一个成员是一个非空的值类型 [英] LINQ error: The null value cannot be assigned to a member with type System.Int32 which is a non-nullable value type

问题描述

我有以下查询：

  VAR的查询=（从table1.Where T1（C =＆GT; c.ServiceID == 2及和放大器; c.IsDeleted == 1）
             从在table2.Where T2（℃= GT; c.RelServiceBonID == t1.RelServiceBonID＆放大器;＆放大器; c.IsDeleted == 1）.DefaultIfEmpty（）
             从在table3.Where T3（℃= GT; c.BonID == t1.BonID＆放大器;＆放大器; c.UserID == 8和;＆放大器; c.IsDeleted == 1）.DefaultIfEmpty（）
             从在table4.Where T4（C =＆GT; c.BonID == t1.BonID＆放大器;＆放大器; c.IsDeleted == 1）
             新选择
             {
                 t3.UserID，t2.SubServiceID，
             }）;query.Dump（）;
 

当我跑，我得到了以下错误：

  

空值不能分配给类型System.Int32一个成员是一个非空的值类型。

的用户名字段是主键，我不能设置为可为空！

我如何传递这个问题？

解决方案

  

的用户ID字段是主键，我不能设置为可为空

由于HVD下面解释，因为你有有效的外部联接，用户名仍然可以为null。除此之外， SubServiceID 也为空。通常它有助于罪魁祸首转换为可空类型：

 新选择
 {
     用户名=（INT？）t3.UserID，
     SubServiceID =（INT？）t2.SubServiceID
 }）;
 

I have following query:

var query = (from t1 in table1.Where(c => c.ServiceID == 2 && c.IsDeleted == 1)
             from t2 in table2.Where(c => c.RelServiceBonID == t1.RelServiceBonID && c.IsDeleted == 1).DefaultIfEmpty()
             from t3 in table3.Where(c => c.BonID == t1.BonID && c.UserID == 8 && c.IsDeleted == 1).DefaultIfEmpty()
             from t4 in table4.Where(c => c.BonID == t1.BonID && c.IsDeleted == 1)
             select new
             {                                  
                 t3.UserID, t2.SubServiceID,
             });

query.Dump();

When I run, I got the following error:

The null value cannot be assigned to a member with type System.Int32 which is a non-nullable value type.

The UserID field is primary key and I can not set that as nullable!

How I can pass this error?

解决方案

The UserID field is primary key and I can not set that as nullable

As hvd explained below, because you effectively have an outer join, UserID can still be null. Besides that, SubServiceID can also be null. Usually it helps to cast the culprit to a nullable type:

 select new
 {                                  
     UserID = (int?)t3.UserID, 
     SubServiceID = (int?)t2.SubServiceID
 });

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