c# - LINQ to SQL running direct SQL for a scalar value -

i trying execute following raw sql linq has no proper support datediff:

var str = @"select isnull(avg(datediff(day, addeddate, presentdate)), 0)               days                 dummytable";

using linq sql, i'm trying output of above statement using:

var numberofdays = math.round(db.executequery<double>(str).firstordefault());

this give me error: specified cast not valid.

what doing wrong?

thanks in advance!

your code must change to:

var numberofdays = db.executequery<int>(str).firstordefault());

you think why? tell you:

return type of datediff in int.so return type of avg int. return type of isnull int too.

references :
datediff avg

isnull try convert type of second expression first expression.

Expalin