Exception Unhandled (System.InvalidOperationException:'ExecuteReader Connection property has not been initialized'

Question

User-2081767517 posted

Hi all. i am new to coding in visual studio(C#). I am using Windows Forms App (.Net Framework). I am currently doing this code but i meant an error. The error is shown in the title. These are my codes

 private void registerbutton_Click(object sender, EventArgs e)

        {

            if (confirmMembersIDmaskedTextBox.Text != string.Empty || enterMembersIDmaskedTextBox.Text != string.Empty || enterNametextBox.Text != string.Empty)

            {

                if (enterMembersIDmaskedTextBox.Text == confirmMembersIDmaskedTextBox.Text)

                {

                    SqlConnection cn = null;

                    SqlCommand cmd = new SqlCommand("select * from LoginTable where username='" + enterNametextBox.Text + "'", cn);

                    SqlDataReader dr = cmd.ExecuteReader();Exception unhandled 

                    if (dr.Read())

                    {

                        dr.Close();

                        MessageBox.Show("Username Already exist please try another ", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

                    }

                    else

                    {

                        dr.Close();

                        cmd = new SqlCommand("insert into LoginTable values(@username,@password)", cn);

                        cmd.Parameters.AddWithValue("username", enterNametextBox.Text);

                        cmd.Parameters.AddWithValue("password", enterMembersIDmaskedTextBox.Text);

                        cmd.ExecuteNonQuery();

                        MessageBox.Show("Your Account is created . Please login now.", "Done", MessageBoxButtons.OK, MessageBoxIcon.Information);

                    }

                }

                else

                {

                    MessageBox.Show("Please enter both password same ", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

                }

            }

            else

            {

                MessageBox.Show("Please enter value in all field.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);

            }

        }

Please help me. Thank you!

Answer 1

User-1716253493 posted

You need to set the connection

SqlConnection cn = null;

Answer 2

User-2081767517 posted

Sorry but how do i connect it?

Answer 3

User-939850651 posted

Hi StarryNight_XD,

If you want to connect to the database and use ADO.NET to perform some operations, you need the correct connection string to instantiate the database connection.

Server=myServerAddress;Database=myDataBase;Trusted_Connection=True;

For example, if you need to connect to the database named Test in the local address. It should be something like:

string connectionString = "Server=.;Database=Test;Trusted_Connection=True;";
SqlConnection conn = new SqlConnection(connectionString);
conn.Open();
SqlCommand cmd = new SqlCommand("query statement...",conn);
......

For more details, you could refer to this document.

https://docs.microsoft.com/en-us/dotnet/api/system.data.sqlclient.sqlconnection.connectionstring?view=dotnet-plat-ext-5.0

Best regards,

Xudong Peng