如何检查用户名是否存在于数据库的特定列中

Question

I'm using C# with an ASP.Net table. I'm trying to check when a user accesses my web app, that their User ID is listed in the column called UserID in a table that is displayed in the web app. If it is not, then I want to redirect them to an error page.

I need this to check when the page is loaded so obviously it needs to be in Page_Load . I just don't know how to call the column in my table and to have it check the User ID.

This is what I have so far:

protected void Page_Load(object sender, EventArgs e)
{            
    if (!Page.IsPostBack)
    {
        string UserID = HttpContext.Current.Request.LogonUserIdentity.Name.Substring(4);
        SQLUserID();

        if (UserID != //'Whatever values are in the UserID column'//)
        {
            Server.Transfer("ErrorPage.aspx");
        }

        SQLCmd = SqlDataSource1.SelectCommand;
        GridView1.DataBind();
    }
}

The string UserID gives me the User ID of the user. SQLUserID() = SELECT UserId FROM Info. I know the way I called that isn't correct but I'm not sure how to do it.

Answer 1

It can help you:

SqlConnection conn = new SqlConnection(connectionString); 
SqlCommand check_User_Name ("SELECT COUNT(*) FROM tblUser WHERE (UserID=@UserID)",conn);
check_User_Name.Parameters.AddWithValue("@UserID,UserID);
int userExist=(int)check_User_Name.ExecuteScalar();
if(userExist>0)
{
    //Login
}
else
{
   Server.Transfer("ErrorPage.aspx");
}

just write your connection string and enjoy it.

Answer 2

So here is how I got it to work below Page_Load

{
string connectionString = "Data Source=###;Initial Catalog=###;Integrated Security=True";
        if (!Page.IsPostBack)                
        {
            using (SqlConnection sqlConnection = new SqlConnection(connectionString))
            {
                sqlConnection.Open();

                using (SqlCommand sqlCommand = new SqlCommand("SELECT COUNT(UserID) from Info WHERE UserID like @UserID", sqlConnection))
                {
                    string UserID = HttpContext.Current.Request.LogonUserIdentity.Name.Substring(4);                        
                    sqlCommand.Parameters.AddWithValue("@UserID", UserID);
                    int userCount = (int)sqlCommand.ExecuteScalar();
                    if (userCount == 0)
                    {
                        Server.Transfer("ErrorPage.aspx");
                    }

                    SQLCmd = SqlDataSource1.SelectCommand;
                    GridView1.DataBind();
                }
            }
        }