[c#] The cast to value type 'Int32' failed because the materialized value is null

I have the following code. I'm getting error:

"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."

when CreditHistory table has no records.

var creditsSum = (from u in context.User
                  join ch in context.CreditHistory on u.ID equals ch.UserID                                        
                  where u.ID == userID
                  select ch.Amount).Sum();

How can I modify the query to accept null values?

To allow a nullable Amount field, just use the null coalescing operator to convert nulls to 0.

var creditsSum = (from u in context.User
              join ch in context.CreditHistory on u.ID equals ch.UserID                                        
              where u.ID == userID
              select ch.Amount ?? 0).Sum();

I see that this question is already answered. But if you want it to be split into two statements, following may be considered.

var credits = from u in context.User
              join ch in context.CreditHistory 
                  on u.ID equals ch.UserID                                        
              where u.ID == userID
              select ch;

var creditSum= credits.Sum(x => (int?)x.Amount) ?? 0;

I was also facing the same problem and solved through making column as nullable using "?" operator.

Sequnce = db.mstquestionbanks.Where(x => x.IsDeleted == false && x.OrignalFormID == OriginalFormIDint).Select(x=><b>(int?)x.Sequence</b>).Max().ToString();

Sometimes null is returned.

Had this error message when I was trying to select from a view.

The problem was the view recently had gained some new null rows (in SubscriberId column), and it had not been updated in EDMX (EF database first).

The column had to be Nullable type for it to work.

var dealer = Context.Dealers.Where(x => x.dealerCode == dealerCode).FirstOrDefault();

Before view refresh:

public int SubscriberId { get; set; }

After view refresh:

public Nullable<int> SubscriberId { get; set; }

Deleting and adding the view back in EDMX worked.

Hope it helps someone.

I have used this code and it responds correctly, only the output value is nullable.

var packesCount = await botContext.Sales.Where(s => s.CustomerId == cust.CustomerId && s.Validated)
                                .SumAsync(s => (int?)s.PackesCount);
                            if(packesCount != null)
                            {
                                // your code
                            }
                            else
                            {
                                // your code
                            }

Got this error in Entity Framework 6 with this code at runtime:

var fileEventsSum = db.ImportInformations.Sum(x => x.FileEvents)

Update from LeandroSoares:

Use this for single execution:

var fileEventsSum = db.ImportInformations.Sum(x => (int?)x.FileEvents) ?? 0

Original:

Changed to this and then it worked:

var fileEventsSum = db.ImportInformations.Any() ? db.ImportInformations.Sum(x => x.FileEvents) : 0;

You are using aggregate function which not getting the items to perform action , you must verify linq query is giving some result as below:

var maxOrderLevel =sdv.Any()? sdv.Max(s => s.nOrderLevel):0