InvalidCastException: The specified cast is invalid?

Question

I have an application that connects to a database and retrieves information (from a table called "Transactions") for a given AccountNo(which is a field in the table). Then it puts the retrieved information into an instance of a class called "Transaction". From that instance of the class it then creates a new node into a pre created generic Doubly Linked List called "Transactions". (I apologise if I have worded anything wrong, I am very new to all of this)

Now my issue is that when I try to put the retrieved information into the instance of the class "Transaction" I get an "InvalidCastException" which says "The specified cast is invalid". All the datatypes are correct so I don't really know what the problem is.

Here is my code.

Transaction class:

public class Transaction
{
    private int AccountNumber;
    private DateTime Date;
    private string Description;
    private string DebitCredit;
    private float Amount;

    public Transaction(int accountNumber, DateTime date, string description, string debitCredit, float amount)
    {
        this.AccountNumber = accountNumber;
        this.Date = date;
        this.Description = description;
        this.DebitCredit = debitCredit;
        this.Amount = amount;
    }
}

The rest of my code is behind a button click event(The line that is throwing the cast error has ** on either side of it):

private void button1_Click(object sender, EventArgs e)
{
    LinkedList<Transaction> Transactions = new LinkedList<Transaction>(); //create the generic linked list
    SqlConnection con = new SqlConnection(@"Data Source=melss002; Initial Catalog=30001622; Integrated Security=True"); //Connection string
    int accNum = Int32.Parse(Microsoft.VisualBasic.Interaction.InputBox("Please enter account number", "Account Number")); //Prompt the user for account number
    SqlCommand cmd = new SqlCommand("Select * From Transactions where AccountNo = " + accNum, con); //command to execute
    con.Open();  //open the connection to the database           
    SqlDataReader reader = cmd.ExecuteReader();

    if (reader.HasRows)//Check if the table has records
    {
        while (reader.Read()) //read all records with the given AccountNo
        {
            **Transaction Transaction001 = new Transaction(reader.GetInt32(0), reader.GetDateTime(1), reader.GetString(2), reader.GetString(3), reader.GetFloat(4));** //New Transaction node
            Transactions.AddFirst(Transaction001);// add the node to the Doubly Linked List (Transactions)
        }
    }
    else
    {
        MessageBox.Show("No records found");
    }

    PrintNodes(Transactions);

    reader.Close();
    con.Close();
}

Answer 1

If all the data types were correct you wouldn't get this error message, they are not:

If you look at this line, you explicitly tell the reader to return fields of a given data type:

Transaction Transaction001 = new Transaction(reader.GetInt32(0), reader.GetDateTime(1), reader.GetString(2), reader.GetString(3), reader.GetFloat(4));

Please make sure that field 0 is actually an Int32, not an Int16 and that field 4 is actually a float, not a double or even a decimal. Decimal types are in most cases the source of errors like that and I bet your problem can be solved by changing from GetFloat to GetDouble.

Answer 2

That could happen if there null values in table. For example if amout is null it will fail to convert to float. Or maybe it's double in database, not float.