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

我试图建立一个登录页面，从SQL Server数据库获取密码和电子邮件。 我想比较密码和电子邮件。

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");
            }
        }
    }
}

我收到此错误消息：

System.Data.SqlClient.SqlException：'必须声明标量变量“ @email”。

我究竟做错了什么？

Answer 1

您的代码是错误的。 您可以使用查询和连接定义SqlDataAdapter ，但是在尝试使用它填充DataTable之前，不对其进行任何其他操作。 不知道@email或@password的值是什么，因为您从不告诉它。

您的代码应如下所示：

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));