DataReader.Read() returning empty

Question

i essentially have a query that generates a list of items (column 1) and their descriptions (column 2). There are 3 different items (out of 170) that do not have a description, so i hard coded my program to adjust for those 3 items. However, whenever my reader gets to the first item that has a null column, the reader is not even able to read the Item. Instead it says "Enumeration Yielded No Results"

var reader = command.ExecuteReader();
while (reader.Read())
{
    var node = reader[0] as string;
    string fullNodeName = string.Empty; 
    if (string.IsNullOrEmpty((string)reader[1]))
    {
        switch ((string)reader[0])
        {
            case "xxx":
                fullNodeName = "jhhfgnfh";
                break;
            case "xxx":
                fullNodeName = "fhnfgndfgdh";
                break;
            case "xxx":
                fullNodeName = "werqrqwerq";
                break;
        }
    }
    else
    {
        fullNodeName = reader[1] as string;
    }
    _nodeTokenList.Add(new Carriers.NodeToken(node, string.Format("{0} - {1}", node, fullNodeName)));

}

the data looks something like

Node   Description

XXX  ||  YYYYYYY YYY YYY

XXX  ||  YYYYYYY YYY YYY

XXX  || YYYYYYY YYY YYY

XXX  ||  YYYYYYY YYY YYY

XXX  ||                

XXX  ||  YYYYYYY YYY YYY

the row with the null description field is when the program starts acting up. Whats weird is that it enters the while loop for this row, but the exception gets caught at var node = reader[0] as string; (the field that is NOT null)

Please pay more attention to code formatting when you ask a question. Most of your code was indented miles over, making it much harder to read. Before posting, always read over what you're about to post and ask yourself whether it's formatted the way you'd want to read it if you were trying to answer. — Jon Skeet
– Jon Skeet, Commented Dec 15, 2016 at 19:41
"Enumeration Yielded No Results" sounds like a debugger message. What happens when you actually run the code? — Jon Skeet
– Jon Skeet, Commented Dec 15, 2016 at 19:42
It captures all of the members up until the row with the empty field then it throws an exception "Unable to cast object of type 'System.DBNull' to type 'System.String'."} ...the yieleded no results is what is stored in the reader when i inspected the variable — Jacob Alley
– Jacob Alley, Commented Dec 15, 2016 at 19:43

gmiley · Accepted Answer · 2016-12-15 20:04:33Z

2

You should swap out the (string)reader[1] with Convert.ToString(reader[1]). It contains a DBNull value, not null, and casting to string is what is causing your error. The Convert class can handle conversion better:

var reader = command.ExecuteReader();
reader.Read();
while (reader.Read())
{
    var node = Convert.ToString(reader[0]);
    string fullNodeName = string.Empty; 
    if (string.IsNullOrEmpty(Convert.ToString(reader[1])))
    {
        switch ((string)reader[0])
        {
            case "xxx":
                fullNodeName = "jhhfgnfh";
                break;
            case "xxx":
                fullNodeName = "fhnfgndfgdh";
                break;
            case "xxx":
                fullNodeName = "werqrqwerq";
                break;
        }
    }
    else
    {
        fullNodeName = reader[1] as string;
    }
    _nodeTokenList.Add(new Carriers.NodeToken(node, string.Format("{0} - {1}", node, fullNodeName)));

}

edited Dec 15, 2016 at 20:04

answered Dec 15, 2016 at 19:52

gmiley

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2 Comments

Jacob Alley Over a year ago

I like this answer but the exception is getting triggered 2 lines above, with var node = reader[0]

gmiley Over a year ago

Updated, just use Convert.ToString() again on the convert of reader[0].

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