LINQ错误:无法将null值分配给类型为System.Int32的成员,该成员是非可空值类型

Question

我有以下查询:

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();

当我运行时,我收到以下错误:

无法将null值分配给类型为System.Int32的成员,该类型是非可空值类型.

该UserID字段是主键,我无法将其设置为可为空!

我怎么能传递这个错误？

Answer 1

UserID字段是主键,我不能将其设置为可为空

正如hvd在下面解释的那样,因为你实际上有一个外连接,UserID所以仍然可以为null.除此之外,SubServiceID也可以为null.通常它有助于将罪魁祸首变为可空类型:

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