從數據庫中獲取一個數據單元

Question

我想從我的數據庫中獲取數據。 表名是MsUser，其中包含用戶ID，用戶名和密碼。 有幾行。

表單描述：我從登錄名開始，需要用戶名和密碼才能登錄。 登錄后打開交易表單，在該表單中，將使用標簽userID基於已登錄的用戶名顯示userId。

如果我的英語不好，這就是我用來匹配用戶名和密碼的代碼。 非常感謝您的幫助。

  private void btnLogin_Click(object sender, EventArgs e)
    {

        SqlConnection cn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=E:\ProgII Project\MoneyManager\MoneyManager\MsUser.mdf;Integrated Security=True;User Instance=True");

        SqlDataAdapter sda = new SqlDataAdapter("Select Count(*) From MsUser where username='"+txtUsername.Text+"' and password='"+txtPassword.Text+"'",cn);

        DataTable dt = new DataTable();
        sda.Fill(dt);
        if (dt.Rows[0][0].ToString()=="1")
            {
                this.Hide();

            }
        else
        {
            MessageBox.Show("your id or password is wrong");
        }

    }

Answer 1

如果您恰好返回一行，一列（如SELECT COUNT(*) ），請使用SqlCommand及其.ExecuteScalar（）方法-無需為單個值帶來DataTable的所有開銷！

使用這樣的東西：

private void btnLogin_Click(object sender, EventArgs e)
{
    // define query - and **ALWAYS** use parameters!
    string query = "SELECT COUNT(*) FROM dbo.MsUser WHERE username = @UserName AND password = @password);";

    // set up connection and command
    using (SqlConnection cn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=E:\ProgII Project\MoneyManager\MoneyManager\MsUser.mdf;Integrated Security=True;User Instance=True"))
    using (SqlCommand cmd = new SqlCommand(query, cn))
    {
        // define parameters and provide values
        cmd.Parameters.Add("@username", SqlDbType.VarChar, 100).Value = txtUserName.Text;
        cmd.Parameters.Add("@password", SqlDbType.VarChar, 100).Value = txtPassword.Text;

        // open connection, execute command, close connection
        cn.Open();
        var result = cmd.ExecuteScalar();
        cn.Close();

        // if result is not null and can be converted to an int....
        if(result != null)
        {
            int userCount;

            if(int.TryParse(result.ToString(), out userCount))
            {
                // OK, you have a good value - if it's > 0, your user entry exists....
                if (userCount > 0)
                {
                    // success - user exists with password
                }
                else 
                {
                    // no success - no such entry
                }
            }
            else
            {
               // you didn't get a numeric value......
            }
        }
        else
        {
            // you didn't get any value......
        }
    }
}

另外：請確保您永遠不要在數據庫表中存儲純文本密碼！

更新：如果您需要檢索UserId （而不只是計數），請使用如下查詢：

string query = "SELECT UserId FROM dbo.MsUser WHERE username = @UserName AND password = @password);";

然后檢查是否返回了有效的UserId （不確定可能是哪種數據類型。...）

var result = cmd.ExecuteScalar();

// checking if we got something (or null)
if (result != null)
{
    string userId = result.ToString();
}
else
{
     // we didn't get any "UserId" back -> invalid combination of "username" and "password"
}

Answer 2

這可能會對您有所幫助，但請注意Sql注入
更新了代碼以防止Sql Injection。

private void btnLogin_Click(object sender, EventArgs e)
{
        SqlConnection cn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=E:\ProgII Project\MoneyManager\MoneyManager\MsUser.mdf;Integrated Security=True;User Instance=True");

        SqlCommand cmd1 = new SqlCommand("Select Count(*) From MsUser where username = @username and password = @passowrd", cn);
        cmd1.Parameters.AddWithValue("@username", idBox.Text.Trim());
        cmd1.Parameters.AddWithValue("@passowrd", passwordBox.Text.Trim());            

        int returnValue = Convert.ToInt32(cmd1.ExecuteScalar());

        if (returnValue == 1)
        {
             this.Hide();
        }
        else
        {
            MessageBox.Show("your id or password is wrong");
        }
 }

Answer 3

假設您的用戶表在每個用戶名和密碼的組合中包含一條唯一的記錄，

private void btnLogin_Click(object sender, EventArgs e)
    {
        string requiredUserId;

        SqlConnection cn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=E:\ProgII Project\MoneyManager\MoneyManager\MsUser.mdf;Integrated Security=True;User Instance=True");

        SqlDataAdapter sda = new SqlDataAdapter("Select Count(userID),UserId From MsUser where username='"+txtUsername.Text+"' and password='"+txtPassword.Text+"' Group By userID",cn);

        DataTable dt = new DataTable();
        sda.Fill(dt);
        if (dt.Rows[0][0].ToString()=="1")
            {
                this.Hide();
                requiredUserId=dt.Rows[0][1].ToString(); //Use this requiredUserId in your next form!!
            }
        else
        {
            MessageBox.Show("your id or password is wrong");
        }

    }