Unable to cast object of type 'System.DBNull' to type 'System.String'

Question

I have a datable code to generate a string, which is sb.ToString().

DataTable dt = dbaccess.GetDataTable("TEST"); // get datatable
List<DataRow> drlist = dt.AsEnumerable().ToList(); // each row only has one element.
StringBuilder sb = new StringBuilder(); 
foreach (DataRow row in drlist)
{
    foreach (string str in row.ItemArray)
    {
        sb.Append(str);
    }
}

The datatable is

You see that there is "NULL" to cause the error "Unable to cast object of type 'System.DBNull' to type 'System.String'. How to fix it?

score 4 · Accepted Answer · answered Apr 30 '12 at 16:14

4

Try this:

foreach (object str in row.ItemArray) 
{ 
    if (DbNull.Value.Equals(str))
       sb.Append("NULL");
    else
       sb.Append(str.ToString()); 
}

answered Apr 30 '12 at 16:14

Brian Mains

50,520
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score 1 · Answer 2 · answered Apr 30 '12 at 16:13

1

Change your loop:

foreach(var obj in row.ItemArray)
{
    if(obj is string) sb.Append(obj as string);
}

answered Apr 30 '12 at 16:13

Justin Niessner

242,243
40
408
536

1

But it sounds like `obj` might be `DbNull`, not `null`, no? – Kirk Woll Apr 30 '12 at 16:14

score 1 · Answer 3 · answered Apr 30 '12 at 16:15

1

            if(!row.IsNull("column"))
            {
                foreach (string str in row.ItemArray)
                {
                    sb.Append(str);
                }                
            }

answered Apr 30 '12 at 16:15

AmandaSai98b

485
1
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17

Unable to cast object of type 'System.DBNull' to type 'System.String'

3 Answers3