Why do I have a NullReferenceException when i am using a IsNull condition?

Question

I have to join 2 different datatable like with linq:

   // let use Linq
        var DateMarket = from p in IndexPrice.AsEnumerable()
                         join q in TickerPrice.AsEnumerable() on p.Field<DateTime>("DATE") equals q.Field<DateTime>("DATE") into UP
                         from q in UP.DefaultIfEmpty()
                         where p.Field<DateTime>("DATE") != null && !q.IsNull("CHG_PCT_1D")
                         select TestRecap.Rows.Add(p.Field<DateTime>("DATE"), q.Field<Double>("CHG_PCT_1D")) ;

however even if I use the condition :

  where p.Field<DateTime>("DATE") != null && !q.IsNull("CHG_PCT_1D")

I still have a NullReferenceException at this line. Do you have an idea why ?

Thanks

Do you have any Rows after joins (in select statement)?

Anatolii Gabuza
– Anatolii Gabuza

2012-01-10 07:56:03 +00:00
Commented Jan 10, 2012 at 7:56 — Anatolii Gabuza
– Anatolii Gabuza, Commented Jan 10, 2012 at 7:56

w5l · Accepted Answer · 2012-01-10 07:58:49Z

1

The from q in UP.DefaultIfEmpty() indicates, that if no matching q is found for your p, it will use the default value, which is null (same as with FirstOrDefault() and SingleOrDefault() functions).

Check for q != null, and it should work.

answered Jan 10, 2012 at 7:58

w5l

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Maheep · Accepted Answer · 2012-01-10 07:54:16Z

0

One among p and q might be null for row after join. Check for their nullification.

where p!=null 
   && p.Field<DateTime>("DATE") != null 
   && q != null 
   && !q.IsNull("CHG_PCT_1D")

answered Jan 10, 2012 at 7:54

Maheep

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