"Unable to case object of type 'System.Decimal' to type 'System.String' occuring within a LINQ statement.

Posted on 2010-11-22
Last Modified: 2013-11-11
The following LINQ statement is generating the error.

                        IEnumerable<String> keyValue = ((IEnumerable<String>)
                            from DataRow rows in dtPrimary.Rows
                            where rows[currentGroup.Peek().ColumnName.ToString()].ToString() == node.ToString()
                            select (String)rows[key]).Take(1).ToArray();

The exception is occuring in the select portion: select (String) rows[key].Take(1).ToArray() due to the fact that several of the columns in dtPrimary are of type System.Decimal. When I initially wrote the code I was only interested in the Strings, however.  Is there away for me to handle this without doing IEnumerable<object>?  It would be best for me just to have all the decimal (or ints) convert to a string so that client code doesn't have to change.


Question by:_Wade_
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LVL 33

Expert Comment

by:Todd Gerbert
ID: 34190558
Try select rows[key].ToString().Take(1).ToArray();

I think that should either give you the string representation of a decimal, or if the value was already a string will just get you that string.

Assisted Solution

_Wade_ earned 0 total points
ID: 34190578

IEnumerable<String> keyValue = ((IEnumerable<String>)
                            from DataRow rows in dtPrimary.Rows
                            where rows[currentGroup.Peek().ColumnName.ToString()].ToString() == node.ToString()
                            select Convert.ToString(rows[key])).Take(1).ToArray();

Please! Please! no one laugh...   I was up late last night.


Thanks to anyone who took the time to read.
LVL 11

Accepted Solution

jasonduan earned 125 total points
ID: 34190605
I would do something like:
IEnumerable<String> keyValue =  (from DataRow row in dt.AsEnumerable()
                    where ...
                    .select row[key].ToString()
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Author Comment

ID: 34190617
No, that gives the exception:

Unable to cast object of type 'WhereSelectEnumarableIterator`2[System.Data.DataRow.System.Object]` to type 'System.Collections.Generic.IEnumerable1[System.String]'.

But thanks for the response tqerbert!
LVL 33

Expert Comment

by:Todd Gerbert
ID: 34190674
Since everything in .Net implements ToString() method, it's always safe to call - I think I just made a typo and missed a parentheses. ;)

Either way, you came to about the same conclusion on your own anyway (I would guess that the implementation of Convert.ToString(Decimal d) mostly just does return d.ToString())
LVL 33

Expert Comment

by:Todd Gerbert
ID: 34190736
Incidentally, I see you're using .Take(1) to get just the first result - if your intention is to retrieve only the value of the first item in the result set, it might make more sense to write:

string result = (from DataRow rows in dtPrimary.Rows
                       where rows[currentGroup.Peek().ColumnName.ToString()].ToString() == node.ToString()
                       select rows[key].ToString()).FirstOrDefault();

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Author Closing Comment

ID: 34221267
Jason, I like your way a little better than mine so I'm marking yours best, but I still get to keep half the points for answering my own question. :)

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