LINQ - Specified cast is not valid with dataview use

Question

I am trying to get the presence of rows based on the passed col. The column is coming from the database as MultiSelect.

bool bCFPresent = IsMultiSelectCFPresent(dvDataTag, "MultiSelect");


public static bool IsPresent(DataView dvDataTag, string colName)
{
  return ((from DataRowView drv in dvDataTag
                     where drv.Row.Field<short>(colName) == 1
                     select drv).Count() > 0 ? true : false);  
}

But I am getting this error:-

System.InvalidCastException was unhandled by user code
Message="Specified cast is not valid." Source="System.Data.DataSetExtensions" StackTrace: at System.Data.DataRowExtensions.UnboxT`1.ValueField(Object value) at System.Data.DataRowExtensions.Field[T](DataRow row, String columnName)

Please help .

What type is 'colName' in the DB? – Nasmi Sabeer May 04 '11 at 12:04 — Nasmi Sabeer, May 04 '11 at 12:04

Daniel Hilgarth · Answer 1 · 2011-05-04T10:41:41.443

1

The problem seems to be that the type of the column named colName can't be casted to a short...
Overall, your code doesn't seem to make a whole lot of sense. The number of rows is the same for each column. Instead, try to check for the column directly, e.g like this:

public static bool IsPresent(DataView dvDataTag, string colName)
{
    return dvDataTag.Table.Columns.Cast<DataColumn>().
                                      Any(c => c.ColumnName == colName);
}

edited May 04 '11 at 10:41

answered May 04 '11 at 10:36

Daniel Hilgarth

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This col is coming as either value 0 or 1 in the dataset. Something weird is happening.. – Karan May 04 '11 at 10:39
I want to get the row count where colName value is 1. – Karan May 04 '11 at 10:44
so, what you really want is: `select count(*) from table where colName = 1`? This should be working with your original code. Maybe try using `int` instead of `short`? – Daniel Hilgarth May 04 '11 at 10:53
I don't know your database, so I really can't say any more. – Daniel Hilgarth May 04 '11 at 11:09
i just checked again with using int. In some places, it is working fine and at some places it is giving the same error. Although, i am returning it as 0 or 1 from the db. Not sure, why this is behaving erratic? – Karan May 04 '11 at 11:26
Are you always providing the same value to `colName`? – Daniel Hilgarth May 04 '11 at 11:28
No, I mean: Does the variable `colName` always contain the same column name? – Daniel Hilgarth May 04 '11 at 11:35
The problem might be, that it does not only contain 0 and 1 but also NULL. Is this a possibility? – Daniel Hilgarth May 04 '11 at 11:38
it cannot be null. It will be either 1 or 0. – Karan May 04 '11 at 11:41
Then I have no idea left, sorry. – Daniel Hilgarth May 04 '11 at 11:44

abhilash · Answer 2 · 2011-05-04T10:54:30.290

0

I'm not really sure what you're trying to do in your predicate

drv.Row.Field<short>(colName) == 1

But your IsPresent Method can be rewritten as

Update:

public static bool IsPresent(DataView dvDataTag, string colName)
{

        return dvDataTag.Any(drv => string.Equals("1",drv[colName].ToString()));
}

For the Row Count

int count =  dvDataTag.Count(drv => string.Equals("1",drv[colName].ToString()));

PS: Handling of nulls is left to the OP

edited May 04 '11 at 10:54

answered May 04 '11 at 10:44

abhilash

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drv need not be defined. Isn't that the fun of using lamdas ? :) – abhilash May 04 '11 at 12:26
i tried to use the row count code given by you. But it is giving this error. Error 2 'System.Data.DataView' does not contain a definition for 'Count' and no extension method 'Count' accepting a first argument of type 'System.Data.DataView' could be found (are you missing a using directive or an assembly reference?) – Karan May 05 '11 at 10:52
@Karan have you included [System.Linq namespace ?](http://msdn.microsoft.com/en-us/library/system.linq.aspx) – abhilash May 09 '11 at 16:46

LINQ - Specified cast is not valid with dataview use

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