Question

我一直收到一个我不明白的错误。必须声明标量变量“@varname”

数小时的研究，尝试了多种解决方案而没有成功。

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，它根据存储在Sql数据库中的信息检查用户是否退出。

这就是我认为问题来自的地方：

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;
}

具体在哪里“dataAdapter.Fill（loginCredentials）;”正在执行。

注释掉的语句在使用正确的用户名和密码登录用户时成功运行，但据我所知，它不安全，因为它容易受到sql注入，这就是我试图参数化sql语句的原因。

错误截图如下：

任何帮助将不胜感激。

Answer 1

您需要将cmd传递给SqlDataAdapter构造函数，而不是cmdString和conn个对象。

Answer 2

编辑：您应该将sqlcommand传递给dataAdapter，因为在您的情况下，sqlcommand（cmd）具有的信息不仅仅是commandtext和connectionstring。您的代码可能如下所示：

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;
}

Answer 3

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

注意uname前面的@。

Answer 4

除了下面描述的所有错误（或者在这里;））..你正在传递命令行和数据适配器的连接，但是你正在填写你没有使用的命令的参数..;）所以你有几个错误......

Answer 5

最重要的是首先检查某个值是否分配给特定变量，即

cmd.parameter.add(@YOUR_VARIABLE, sqlDbtype.TYPE).value = ValueYouwantToGIveToThatVariable;

必须声明标量变量“@UserName”

5 个答案: