必须声明标量变量"@UserName"； [英] Must declare the scalar variable "@UserName"

问题描述

我不断收到我不明白的错误. 必须声明标量变量"@varname"

I keep getting an error that i dont understand. Must declare the scalar variable "@varname"

数十小时的研究，没有成功地尝试了多种解决方案.

Tens of hours of research, tried multiple solutions without sucess.

我的目标是创建一个使用2个文本框和一个按钮的登录页面，该按钮将根据Sql数据库中存储的信息检查用户是否退出.

My aim is to create a login page that uses 2 textboxes, and a button, where it checks if the user exits based on the information stored in a Sql Database.

这是我认为问题出在哪里:

This is where i think the problem is coming from:

private bool DBConnection(string userName, string password)
{
    SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);

    //string cmdString = ("SELECT UserName, Password FROM Users WHERE UserName ='" + userName +
    //                    "'AND Password ='" + password + "'");         //REMOVED AS THIS IS PRONE TO SQL INJECTIONS

    string cmdString = ("SELECT * FROM Users WHERE UserName = @uname AND Password = @pw");

    SqlCommand cmd = new SqlCommand(cmdString, conn);

    cmd.Parameters.Add("uname", SqlDbType.VarChar).Value = userName;
    cmd.Parameters.Add("pw", SqlDbType.VarChar).Value = password;

    DataSet loginCredentials = new DataSet();
    SqlDataAdapter dataAdapter;

    try
    {
        if (conn.State.Equals(ConnectionState.Closed))
        {
            conn.Open();

            dataAdapter = new SqlDataAdapter(cmdString, conn);
            dataAdapter.Fill(loginCredentials);

            conn.Close();

            if (loginCredentials != null)
            {
                if (loginCredentials.Tables[0].Rows.Count > 0)
                {
                    return true;
                }
                else
                {
                    lblMessage.Text = "Incorrect Username or Password";
                    lblMessage.Visible = true;
                }
            }   
        }
    }
    catch (Exception err)
    {
        lblMessage.Text = err.Message.ToString() + " Error connecting to the Database // " + cmd.Parameters.Count;
        lblMessage.Visible = true;
        return false;
    }

    return false;
}

特别是在"dataAdapter.Fill(loginCredentials);"所在的位置正在执行.

specifically where the "dataAdapter.Fill(loginCredentials);" is being executed.

已注释掉的语句成功登录了具有正确用户名和密码的用户，但据我所知这是不安全的，因为它容易受到sql注入的攻击，这就是为什么我要参数化sql语句的原因.

the commented out statement works successfully in logging in a user with correct username and password, but as far as i know is not secure, as its vulnerable to sql injections and this is why i'm trying to parameterize the sql statement.

错误截图如下:

任何帮助将不胜感激.

推荐答案

您应该将sqlcommand传递给dataAdapter，因为在您的情况下sqlcommand(cmd)具有比仅命令文本更多的信息，并且连接字符串.您的代码可能如下所示:

You should pass the sqlcommand to the dataAdapter because in your case the sqlcommand (cmd) has more information than mere commandtext and connectionstring. Your code may look like the following:

private bool DBConnection(string userName, string password)
{
 SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);

//string cmdString = ("SELECT UserName, Password FROM Users WHERE UserName ='" + userName +
//                    "'AND Password ='" + password + "'");         //REMOVED AS THIS IS PRONE TO SQL INJECTIONS

string cmdString = ("SELECT * FROM Users WHERE UserName = @uname AND Password = @pw");

SqlCommand cmd = new SqlCommand(cmdString, conn);

cmd.Parameters.Add("uname", SqlDbType.VarChar).Value = userName;
cmd.Parameters.Add("pw", SqlDbType.VarChar).Value = password;

DataSet loginCredentials = new DataSet();
SqlDataAdapter dataAdapter;

try
{
    if (conn.State.Equals(ConnectionState.Closed))
    {
        conn.Open();

        dataAdapter = new SqlDataAdapter(cmd);
        dataAdapter.Fill(loginCredentials);

        conn.Close();

        if (loginCredentials != null)
        {
            if (loginCredentials.Tables[0].Rows.Count > 0)
            {
                return true;
            }
            else
            {
                lblMessage.Text = "Incorrect Username or Password";
                lblMessage.Visible = true;
            }
        }   
    }
}
catch (Exception err)
{
    lblMessage.Text = err.Message.ToString() + " Error connecting to the Database // " + cmd.Parameters.Count;
    lblMessage.Visible = true;
    return false;
}

return false;
}

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