尝试将文本框中的数据与数据库中的数据进行比较时出现错误消息

Question

I'm trying to make a login page where I take the Password and Email from a SQL Server database. I want to compare the password and the Email.

private void buttoninloggen_Click(object sender, EventArgs e)
{
    using (SqlConnection connection = new SqlConnection(connectionstring))
    {
        connection.Open();

        string emailinlog = textBoxEmailLogin.Text;
        string passwordinlog = textBoxPasswordLogin.Text;
        string vergelijken = "select * from Account where Email = @email and Password = @password";

        SqlDataAdapter adapter = new SqlDataAdapter(vergelijken, connection);

        MessageBox.Show("tot hier is t goed");

        using (SqlCommand ophalen = new SqlCommand(vergelijken, connection))
        {
            ophalen.Parameters.AddWithValue("@email", emailinlog);
            ophalen.Parameters.AddWithValue("@password", passwordinlog);

            DataTable tafel = new DataTable();
            adapter.Fill(tafel);

            if (tafel.Rows.Count > 0)
            {
                MessageBox.Show("ingelogd");
            }
        }
    }
}

I get this error message:

System.Data.SqlClient.SqlException: 'Must declare the scalar variable "@email".'

What am I doing wrong?

Answer 1

Your code is wrong. You define an SqlDataAdapter with the query and connection but then do nothing else with it before trying to use it to fill the DataTable . It has no idea what the values for @email or @password are because you never tell it.

Your code should look like this:

private void buttoninloggen_Click(object sender, EventArgs e)
{
    using (SqlConnection connection = new SqlConnection(connectionstring))
    {
        connection.Open();
        string emailinlog = textBoxEmailLogin.Text;
        string passwordinlog = textBoxPasswordLogin.Text;
        string vergelijken = "select * from Account where Email = @email and Password = @password";

        // Moved the 'SqlDataAdapter' further down
        // SqlDataAdapter adapter = new SqlDataAdapter(vergelijken, connection);

        MessageBox.Show("tot hier is t goed");
        using (SqlCommand ophalen = new SqlCommand(vergelijken, connection))
        {
            ophalen.Parameters.AddWithValue("@email", emailinlog);
            ophalen.Parameters.AddWithValue("@password", passwordinlog);
            DataTable tafel = new DataTable();

            // SqlDataAdapter is now here
            // As it has been passed the SqlCommand it understands the parameters
            // Wrapped in using statement for disposal
            using (SqlDataAdapter adapter = new SqlDataAdapter(ophalen))
            {
                adapter.Fill(tafel);
                if (tafel.Rows.Count > 0)
                {
                    MessageBox.Show("ingelogd");
                }
            }
        }
    }
}

Answer 2

考虑从我的程序中将语法更改为工作代码：

ophalen.Parameters.Add(new SqlParameter("@email", emailinlog));