Specified cast is not valid in foreach

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Hi All,

I trying to group types and its severties on datatable using linq

C#

var query = from row in dt_cv.AsEnumerable()
             group row by new { severity = row.Field<string>("Severity"), 
                          type = row.Field<DateTime>("Type") } into sev
              select new
               {
                Type = sev.Key.type,
                severity = sev.Key.severity,
                sev_count = sev.Count()
               };

When I am trying to get the value of query in foreach loop, it is throwing 'Specified cast is not valid'

C#

foreach (var res in query)
{
  dt.Rows.Add(new object[] { res.Type, res.severity, res.sev_count });
}

Please help.

Thanks in advance

Posted 9-Apr-15 20:43pm

srmohanr

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Tomas Takac 10-Apr-15 3:07am

You are casting Type to DateTime and Severity to string. Check if those casts are valid.

srmohanr 10-Apr-15 4:29am

Thanks Tomas.. I have changed the type from DateTime to String and it works.

2 solutions

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OriginalGriff · Answer 1 · 2015-04-09T21:39:00

As Tomas says, it's the cast in your Linq query that causes the problem. It occurs in the foreach because Linq code is not executed immediately - it is a deferred execution system. When you try to use the query results by including it as a target in the foreach expression, that causes the query to be executed - and so the cast operations happen as part of the foreach.

So as suggested, check your datatypes - the source datatable columns and make sure that casting the "Type" column to a DateTime is valid - I would suspect not, given it's name!

Maciej Los · Answer 2 · 2015-04-09T22:37:00

Solution 2

First of all, OriginalGriff is right.
Secondly, i'd suggest to use CopyToDataTable()[^] method instead foreach loop.

Posted 9-Apr-15 22:37pm

Maciej Los