Question

我目前正在尝试这样做，当您在我的网站上创建新用户时，如果名称已经存在，则应该在数据库表brugere中检查，如果已存在，则不应该检查创建一个新用户。

但我无法让它发挥作用......

bool exists = false;

// create a command to check if the username exists
using (SqlCommand cmd1 = new SqlCommand())

cmd.CommandText = "select count(*) from brugere where bruger_navn = @bruger_navn";
{
    cmd.Parameters.AddWithValue("bruger_navn", txtUsername.Text);
    exists = (int)cmd.ExecuteScalar() > 0;
}

// if exists, show a message error
if (exists)
    Label1. Text = "This username has been using by another user."; 
else
{
    // does not exists, so, persist the user
    using (SqlCommand cmd2 = new SqlCommand())
        cmd2.CommandText = @"INSERT INTO brugere (bruger_navn, Bruger_pass) VALUES (@bruger_navn, @bruger_pass)";
    {
        cmd.Parameters.AddWithValue("bruger_navn", txtUsername.Text);
        cmd.Parameters.AddWithValue("bruger_pass", txtPassword.Text);

        cmd.ExecuteNonQuery();
    }
}

conn.Close();

Answer 1

首先，您在参数名称

之前缺少@

cmd.Parameters.AddWithValue("@bruger_navn", txtUsername.Text);
....
cmd.Parameters.AddWithValue("@bruger_navn", txtUsername.Text);
cmd.Parameters.AddWithValue("@bruger_pass", txtPassword.Text);

此外，您需要为Connection

指定SqlCommand属性

using (SqlCommand cmd1 = new SqlCommand())
{
   cmd1.Connection = conn;

或

using (SqlCommand cmd1 = conn.CreateCommand())
{

此外，你有一些大括号和变量名称的混乱，因为我认为代码应该类似于

bool exists = false;

// create a command to check if the username exists
using (SqlCommand cmd1 = conn.CreateCommand())
{
    cmd1.CommandText = "select count(*) from brugere where bruger_navn = @bruger_navn";
    cmd1.Parameters.AddWithValue("bruger_navn", txtUsername.Text);
    exists = (int)cmd1.ExecuteScalar() > 0;
}

// if exists, show a message error
if (exists)
   Label1. Text = "This username has been using by another user."; 
else
{
    // does not exists, so, persist the user
    using (SqlCommand cmd2 = conn.CreateCommand())
    {
        cmd2.CommandText = @"INSERT INTO brugere (bruger_navn, Bruger_pass) VALUES (@bruger_navn, @bruger_pass)";
        cmd2.Parameters.AddWithValue("bruger_navn", txtUsername.Text);
        cmd2.Parameters.AddWithValue("bruger_pass", txtPassword.Text);

        cmd2.ExecuteNonQuery();
    }
}

conn.Close();

检查用户名是否已存在于数据库中c＃

1 个答案: