The cast to value type 'Double' failed because the materialized value is null

问题

CODE:

double cafeSales = db.InvoiceLines
    .Where(x =>
        x.UserId == user.UserId &&
        x.DateCharged >= dateStart &&
        x.DateCharged <= dateEnd)
    .Sum(x => x.Quantity * x.Price);

ERROR:

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

WHAT I HAVE SEEN ALREADY:

The cast to value type 'Int32' failed because the materialized value is null

The cast to value type 'Decimal' failed because the materialized value is null

WHAT I HAVE TRIED:

double cafeSales = db.InvoiceLines
    .Where(x =>
        x.UserId == user.UserId &&
        x.DateCharged >= dateStart &&
        x.DateCharged <= dateEnd)
    .DefaultIfEmpty()
    .Sum(x => x.Quantity * x.Price);

And:

double? cafeSales = db.InvoiceLines
    .Where(x =>
        x.UserId == user.UserId &&
        x.DateCharged >= dateStart &&
        x.DateCharged <= dateEnd)
    .Sum(x => x.Quantity * x.Price);

Neither of these work. I know the cause of the problem is that there are no rows in that table for the UserId I am passing in. In that case, I would prefer Sum() just returned a 0 to me. Any ideas?

回答1:

Best Solution

double cafeSales = db.InvoiceLines
                     .Where(x =>
                                x.UserId == user.UserId &&
                                x.DateCharged >= dateStart &&
                                x.DateCharged <= dateEnd)
                     .Sum(x => (double?)(x.Quantity * x.Price)) ?? 0;

回答2:

You can check if the collection has any correct results.

double? cafeSales = null;
var invoices = db.InvoiceLines
    .Where(x =>
        x.UserId == user.UserId &&
        x.DateCharged >= dateStart &&
        x.DateCharged <= dateEnd
    )
    .Where(x => x.Quantity != null && x.Price != null);
if (invoices.Any()) {
    cafeSales = invoices.Sum(x => x.Quantity * x.Price);
}

回答3:

I know this is a bit old but just in case it helps anyone.

@Matt I guess the DefaultIFEmpty() method should work for you just in case you pass a default value for the column that you are applying Sum onto. This method has some overloads which you might want to check and I suggest type-casting if overloads do not support your requirement.

 (query).DefaultIfEmpty(0)

回答4:

This should do the trick (you may have to remove one of the conditions if either Quantity or Price are not nullable):

var cafeSales = db.InvoiceLines
    .Where(x =>
        x.UserId == user.UserId &&
        x.DateCharged >= dateStart &&
        x.DateCharged <= dateEnd &&
        x.Quantity != null &&
        x.Price != null);

double cafeSalesTotal = 0;

if (cafeSales.Any())
{
    cafeSalesTotal = cafeSales.Sum(x => x.Quantity * x.Price);
}

回答5:

 var cafeSales = db.InvoiceLines
.Where(x =>
    x.UserId == user.UserId &&
    x.DateCharged >= dateStart &&
    x.DateCharged <= dateEnd)
.Sum(x => x.Quantity * x.Price);

double i;
if(cafeSales==null) ? i=0 : i=(double)cafeSales.First();

回答6:

The solutions above didn't work for me. My problem was similar. I was sure that no rows were being returned but Sum behaves in some strange way. So I decided to add a check just before calling the lambda expression where I check for count property of rows returned by the lambda. If it is greater than zero, then I call the sum expression. That worked for me.

回答7:

join sim in ctx.EF.Collaterals on new { id = ini.cam.id, Type = 0 } equals new 
{ id = sim.CampaignId == null ? new Guid() : sim.CampaignId, sim.Type } 
into tempcoll
from sim in tempcoll.DefaultIfEmpty()

This solution works.Actually You need to use ternary operator to check the value and insert Guid if null in the second column and in the second table.and it will work. "The cast to value type 'Double' failed because the materialized value is null" will be solved Thanks

来源：https://stackoverflow.com/questions/15297925/the-cast-to-value-type-double-failed-because-the-materialized-value-is-null

标签

entity-framework