Question

I am trying to run a stored procedure and for some reason it keeps telling me "Specified cast is not valid". the “hidSelectedExpenseIDs” is a hidden field that gets populated with a javascript array of id’s.

Example: the "hidSelectedExpenseIDs.Value" would look like “123,124,125,126”. Hence why I have the .Split(',') in there.

Here is my code:

public void hasExhistingExpenseInvoice()
{
    string[] Expenses = hidSelectedExpenseIDs.Value.Split(',');

    //check if there is an existing invoice. Then report back to the user so the
    //user knows if he/she has to check overwrite option.
    bool invoiceExists = false;

    foreach (var expense in Expenses)
    {
        var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["OSCIDConnectionString"].ToString());
        var command = new SqlCommand("p_CaseFiles_Expenses_InvoiceExhists", connection);
        command.Parameters.Add(new SqlParameter("@ExpenseID", SqlDbType.Int));
        command.Parameters["@ExpenseID"].Value = Convert.ToInt32(expense);
        command.CommandType = CommandType.StoredProcedure;
        try
        {
            connection.Open();
            invoiceExists = (bool)command.ExecuteScalar();
            if (invoiceExists)
            {
                //previous invoice exhists
                Warning1.Visible = true;
                Warning1.Text = "There is an exhisting Invoice.";
            }
        }
        catch (SqlException sql)
        {
            lblStatus.Text = "Couldn't connect to the Database - Error";
            lblStatus.ForeColor = System.Drawing.Color.Red;
        }
        catch (Exception ex)//catches exception here
        {
            lblStatus.Text = "An error occured";
            lblStatus.ForeColor = System.Drawing.Color.Red;
        }
        finally
        {
            if (connection.State == ConnectionState.Open)
                connection.Close();
        }
    }
}

this is my stored procedure:

ALTER PROCEDURE dbo.[InvoiceExhists]
@ExpenseID int
AS
BEGIN
    SELECT InvNumber FROM dbo.Expenses from ExpID = @ExpenseID
END

Answer 1

The logic is faulty.

Your Query returns a number, and you are trying to cast it directly to a Boolean, this can’t be done in C#.

Some languages will interpret any non-zero as true, it is not the case for C# and it will throw an exception.

You will need to compare the returned value.

In this case, you should just check if there is a value, because NULL will be returned if the invoice does not exist.

This would look like this :

invoiceExists = command.ExecuteScalar() != null ;

Also I recommend reading this thread and consider using UDF instead of scalar Stored Procedures.