How to fix 'Cannot convert from 'string' to System.Data.SqlDbType' in a Windows Forms Application

Question

This only happens when I created a basic login screen for a sample application I'm building. I have various other functions in the application that read/write/update rows in a database without errors.

private void btnLogin_Click(object sender, EventArgs e)
    {
        try
        {
            if(txtUname.Text == "" && txtPW.Text == "")
            {
                MessageBox.Show("Please fill in required fields!");
            }
            else
            {
                SqlCommand cmd = new SqlCommand("select * from LoginUsers where U_Name=@Name and U_Pass=@Pass", con);

                cmd.Parameters.Add("@Name", txtUname.Text); <- Error on textbox string
                cmd.Parameters.Add("@Pass", txtPW.Text);    <- Error on textbox string

                SqlDataAdapter adpt = new SqlDataAdapter(cmd);
                DataSet ds = new DataSet();
                adpt.Fill(ds);

                int count = ds.Tables[0].Rows.Count;
                if(count == 1   )
                {
                    MessageBox.Show("Successfully Logged in!");
                }
                else
                {
                    MessageBox.Show("Incorrect username or password!");
                }
            }

        }
        catch(Exception ex)
        {
            MessageBox.Show(ex.Message);
        }

    }

Have you looked up the data type of the second argument? It's not asking for a string. — gunr2171, Jul 06 '22 at 16:43
[sqlparametercollection.add](https://learn.microsoft.com/en-us/dotnet/api/system.data.sqlclient.sqlparametercollection.add?view=dotnet-plat-ext-6.0) - Check the documentation for help. — Ryan Wilson, Jul 06 '22 at 16:44

score 0 · Accepted Answer · edited Jul 06 '22 at 18:35

0

Try anyone from below:

Approach 1:

command.Parameters.Add("@ID", SqlDbType.Int).Value = customerID;

Approach 2:

command.Parameters.AddWithValue("@demographics", demoXml);

Just a random code based on the classification defined, Do let me know if you still face an issue after using any of the above mentioned approach.

edited Jul 06 '22 at 18:35

Charlieface

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answered Jul 06 '22 at 16:46

dLcreations

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Please do not recommend using `AddWithValue`. https://blogs.msmvps.com/jcoehoorn/blog/2014/05/12/can-we-stop-using-addwithvalue-already/ – gunr2171 Jul 06 '22 at 16:48
What is wrong with AddWithValue, that is what actually solved my issue. – AddieCaddy Jul 06 '22 at 16:52
@AddieCaddy - It's to avoid the Type Mismatch issue. and most of the time, these types of mismatches don’t matter if you are sure about what you are passing. Correct gunr2171 ? – dLcreations Jul 06 '22 at 16:56
@AddieCaddy The first option is the one you always want, at least when it comes to strings, dates and decimals – Charlieface Jul 06 '22 at 18:35

How to fix 'Cannot convert from 'string' to System.Data.SqlDbType' in a Windows Forms Application

1 Answers1