Linq错误：强制转换为值类型'Int32'，因为物化值为null

Question

... But it's not null.

FYI - Many threads exist on this error, but none that I've seen using an anonymous type.

I'm Getting an odd InvalidOperationException in a Linq query.

message: "The cast to value type 'Int32' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type."

The confusing thing is that it's erroring when creating an anonymous type:

var workstepid = 484,449;

var wsData = ion.xWorkSteps
   .Where(w => w.WorkStepId == workstepId)
   .Select(w => new
   {
       w.WorkStepId,
       w.ServiceId,
       w.Service.TitleId,
       w.Service.Title.OrderId,
       w.Service.Title.AltTitleId
   }).SingleOrDefault();

In LinqPad this particular query runs just fine and the workstepId used returns an integer value for each property of the anonymous type. So why a casting error when there is no null value for any property!?

FYI, the last property AltTitleId is a nullable int, and the other properties are ints. Also, this code was written weeks ago and I didn't get this error until today. Is something funky w/ my EF?

Edit: SOLVED

We use soft-delete in our db's, setting deleted records to Acive=0. It turns out that there is a property set in EF on the edmx tables filtering out inactive records (filter for Active=1). Naturally, this wouldn't effect Linqpad which gives me the expected result, but since this was an older record I was testing, the title record (Service.Title) had been marked Active=0 and was therefore returning null.

Thanks to everyone for the help.

Answer 1

var workstepid = 484,449;

var wsData = ion.xWorkSteps
   .Where(w => w.WorkStepId == workstepId)
   .Select(w => new
   {
      w.WorkStepId.Value,
      w.ServiceId.Value,
      w.Service.TitleId.Value,
      w.Service.Title.OrderId.Value,
      w.Service.Title.AltTitleId.Value
   }).SingleOrDefault();

Hi you need to add .Value in your int data type to accept null value. hope this helps

Answer 2

如果w.WorkStepId可为空，请尝试将变量设置为...

int? workstepid = 484449;

Answer 3

I suppose, the problem is in your SingleOrDefault().

I suppose that you get 0 records:

var workstepid = 484,449;

var len = ion.xWorkSteps
   .Where(w => w.WorkStepId == workstepId)
   .Length();

And then the anonymouse type must be replace by Default (this is what SingleOrDefault do), but there is no default for your anonymous type.

Try to change it to:

    var wsData = ion.xWorkSteps
   .Where(w => w.WorkStepId == workstepId)
   .Select(w => new
   {
       w.WorkStepId,
       w.ServiceId,
       w.Service.TitleId,
       w.Service.Title.OrderId,
       w.Service.Title.AltTitleId
   })
   .Take(1)
   .ToArray();

Answer 4

May be there are no Service/Title/Order id somewhere, but if it declared as int anonymous type expect int (not nullable), but from database it returns null. Try to rewrite as :

var workstepid = 484,449;

var wsData = ion.xWorkSteps
   .Where(w => w.WorkStepId == workstepId)
   .Select(w => new
   {
     WorkStepId = (int?)w.WorkStepId,
     ServiceId = (int?)w.ServiceId,
     TitleId = (int?)w.Service.TitleId,
     OrderId = (int?)w.Service.Title.OrderId,
     w.Service.Title.AltTitleId
   }).SingleOrDefault();