Unable to cast object of type 'system.int32' to type 'system.string'.

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int Number = int.Parse(dr.GetString(0));
               combocustomer.Items.Add(Number);

find the above code , am going to fetch the customer_ID from DB to front end dropdown ..

whule featching data am facing this error messahe .

can you please help me for the same

What I have tried:

combocustomer.Items.Clear();
           con.Open();
           string str = "select * from Tblcustomer";
           SqlCommand cmd = new SqlCommand(str, con);
           SqlDataReader dr = cmd.ExecuteReader();
           while (dr.Read())
           {
               int Number = int.Parse(dr.GetString(0));
               combocustomer.Items.Add(Number);
           }
           con.Close();

Posted 24-May-20 12:40pm

Member 11297177

Updated 24-May-20 23:27pm

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Garth J Lancaster · Answer 1 · 2020-05-24T18:47:00

Well it could be time to learn how to debug, ie, set a break-point in code then single-step and also think about the code you have written ..

I'd say from a quick look, that

int Number = int.Parse(dr.GetString(0));

could be problematic, one would have to wonder why you're getting the number as a string (which the error messages is saying 'I cant do that') - then parsing it

.. If the column in the database IS numeric, let's assume an integer, then why not

int Number = (dr.GetInt32(0));

??

Also, if you're going to post question(s) about a database, did you not think to include a brief definition of the relevant table ?

Maybe you could also study whatever reference materials you have or google 'C# datareader' to see how to get columns of various data-types

Maciej Los · Answer 2 · 2020-05-24T23:28:00

In addition to solution #1 by Garth J Lancaster
Why to load full table instead of interesting part only?
Replace this:

SQL

select * from Tblcustomer

with:

SQL

select NameOfFieldYouWantToGet from Tblcustomer

BTW: ComboBox[^] control has several useful properties, such as:
DataSource Property (System.Windows.Forms) | Microsoft Docs[^]
DisplayMember Property (System.Windows.Forms) | Microsoft Docs[^]
ValueMember Property (System.Windows.Forms) | Microsoft Docs[^]

Conclusion: If you want to load customer data, you can do that this way:

C#

DataTable dt = new DataTable();
string str = "select CustomerID, CONCAT(LastName, ' ', LEFT(FirstName, 1)) AS CustomerName from Tblcustomer";
SqlCommand cmd = new SqlCommand(str, con);
SqlDataReader dr = cmd.ExecuteReader();
dt.Load(dr);
combocustomer.ValueMember = "CustomerID"
combocustomer.DisplayMember = "CustomerName";
combocustomer.DataSource = dt;

Final note: use using(disposable_object do = new disposable_object) statement to "auto-manage" disposable objects. See: Using objects that implement IDisposable | Microsoft Docs[^]

C#

DataTable dt = new DataTable()
using(SqlConnection connection = new SqlConnection("connectionstring_here"))
{
    connection.Open()
    using(SqlCommand command = new SqlCommand("commandtext_here"), connection)
        using(SqlDataReader reader = command.ExecueReader())
            dt.Load(reader)
    connection.Close()
}
//further instructions here

Unable to cast object of type 'system.int32' to type 'system.string'.

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