Question

这是我的代码，我需要从数据库中检索LoginPassword

public partial class frmPassword : Form
{
    SqlConnection connection = new SqlConnection(@"Data Source=WORKSTATION\SQLEXPRESS;Initial Catalog=TPSystem;Integrated Security=True");

    public frmPassword()
    {
        InitializeComponent();
    }

    private void btnUpdatePassword_Click(object sender, EventArgs e)
    {
        frmLogin login = new frmLogin();
        string UserN = login.UName;
        string Pass;
        SqlCommand cmd = new SqlCommand("SELECT Login_Password FROM AdminLogin WHERE Login_Username = '"+UserN+"'", connection);

        try
        {
            connection.Open();
            SqlDataReader reader = cmd.ExecuteReader();
            reader.Read();

            Pass = reader["Login_Password"].ToString();

            if (tbOldPassword.Text == Pass)
                MessageBox.Show("Password matches");
            else
                MessageBox.Show("Password wrong");
            reader.Close();
        }
        catch (SqlException ex)
        {
            MessageBox.Show(ex.Message, "Report", MessageBoxButtons.AbortRetryIgnore, MessageBoxIcon.Error);
        }
        finally
        {
            connection.Close();
        }
    }
}

执行时出现此错误：

未处理的类型＆＃39; System.InvalidOperationException＆＃39;   发生在System.Data.dll
中
其他信息：无效尝试   在没有数据时读取。

Answer 1

reader.Read()方法返回一个布尔值来指示实际上是否读过任何内容 - 你根本就没有检查过....

将您的代码更改为：

if(reader.Read())
{
    Pass = reader["Login_Password"].ToString();

    if (tbOldPassword.Text == Pass)
            MessageBox.Show("Password matches");
    else
            MessageBox.Show("Password wrong");
}

如果没有读到任何内容，我猜你的用户不存在 - 我不确定你在那种情况下想做什么......由你决定

但请告诉我你不以明文存储密码>在您的数据库中!!!!

Answer 2

似乎数据库中没有您要检查的用户名的条目。请检查是否有结果返回结果：

public partial class frmPassword : Form
{
    SqlConnection connection = new SqlConnection(@"Data Source=WORKSTATION\SQLEXPRESS;Initial Catalog=TPSystem;Integrated Security=True");

    public frmPassword()
    {
        InitializeComponent();
    }

    private void btnUpdatePassword_Click(object sender, EventArgs e)
    {
        frmLogin login = new frmLogin();
        string UserN = login.UName;
        string Pass;
        SqlCommand cmd = new SqlCommand("SELECT Login_Password FROM AdminLogin WHERE Login_Username = '"+UserN+"'", connection);

        try
        {
            connection.Open();
            SqlDataReader reader = cmd.ExecuteReader();
            while(reader.Read())
            {
            Pass = reader["Login_Password"].ToString();

            if (tbOldPassword.Text == Pass)
                MessageBox.Show("Password matches");
            else
                MessageBox.Show("Password wrong");
            }
            reader.Close();
        }
        catch (SqlException ex)
        {
            MessageBox.Show(ex.Message, "Report", MessageBoxButtons.AbortRetryIgnore, MessageBoxIcon.Error);
        }
        finally
        {
            connection.Close();
        }
    }
}

我尝试从数据库中检索密码时出现InvalidOperationException：“无数据存在时无效尝试读取”。

2 个答案: