How do I translate this query string to linq

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string query = "select isnull(sum(amount),0) [amount] from Recharge.dbo.AirtimePromoTable";

i have a project full of raw query string and connection string and now i was task to create entity framework for the project.
How do i check for ISNUll and sum using LINQ to SQL

What I have tried:

Here is what i have tried but its not working...

using (var Context = new RechargeEntities())
      {
        var Que = (from b in Context.AirtimePromoTables
                      .Select(b => b.Amount)
                      .DefaultIfEmpty(0)
                      .Sum().ToString());
      }

Posted 6-May-18 21:44pm

wizklaus

Updated 6-May-18 23:09pm

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Maciej Los · Accepted Answer · 2018-05-06T23:11:00

Solution 1

This should work:

C#

using (var Context = new RechargeEntities())
      {
        var Que = Context.AirtimePromoTables
                      .Sum(b => b.Amount);
      }

[EDIT]
You don't need to check whetever amount is null or not. You don't even need to convert nulls to zeros to be able to sum it up, because Enumerable.Sum Method (IEnumerable(Nullable(Double))) (System.Linq)[^] accepts nullable values as an input parameter.
So, using:

.Sum(b => b.Amount!=null ? b.Amount : 0);

is redundant!

Check this:

C#

double?[] amounts = {null, null};
var result = amounts.Sum(); //returns 0 (zero)

or

C#

double?[] amounts1 = {null, 2.5, 1.5, 0.5, 0.25, 1.75, 3.0, null};
var result1 = amounts.Sum(); //returns 9.5

Good luck!

Posted 6-May-18 23:11pm

Maciej Los

Updated 7-May-18 0:41am

v3

Comments

wizklaus 7-May-18 6:12am

Thanks Maciej for your reply... But it doesn't check if the value ISNULL

Maciej Los 7-May-18 6:28am

What?
Sum method accepts nullable value as parameter. So, you don't need to convert null into zero...
Check this:

double?[] amounts = {null, 2.5, 1.5, 0.5, 0.25, 1.75, 3.0, null};
var result = amounts.Sum();
//9.5

In case of nulls only, sum will return zero!

Karthik_Mahalingam 7-May-18 7:13am

5

Maciej Los 7-May-18 7:51am

Thank you, Karthik.

Wendelius 7-May-18 11:24am

Nise, a 5.

Maciej Los 7-May-18 13:43pm

Thank you, Mika.