如何使用c＃.net将行索引用作数据集索引

Question

I am newbie to c# I am working on project i am trying to loop through data table containing distinct values and my database has song id like:1,2,3,4,6,8,9,10 but dataset takes this values as 0,1,2,3,4,5,6,7 respectively... thanks

String sql = "select  title, song_id from up_song where Song_type='Mp3 Tracks' ";
    adpt = new SqlDataAdapter(sql, cn);
    ds = new DataSet();

    adpt.Fill(ds, "title");
    var maxvalue = ds.Tables["title"].AsEnumerable().Max(x => x.Field<int>("song_id"));
    var minvalue = ds.Tables["title"].AsEnumerable().Min(x => x.Field<int>("song_id"));
    for (i =maxvalue; i >= minvalue; --i)
        {
            try
            {
                hyperlink[i] = new HyperLink();
                hyperlink[i].ID = "hyperlink" + i;
                hyperlink[i].Text = ds.Tables["title"].Rows[i].ItemArray[0].ToString();
                hyperlink[i].NavigateUrl = "Downloadpage.aspx";
                hyperlink[i].ForeColor = System.Drawing.Color.White;
                Panel1.Controls.Add(hyperlink[i]);
                Panel1.Controls.Add(new LiteralControl("<br>"));
                HttpCookie coo = new HttpCookie("song");
                coo["sogtit"] = ds.Tables["title"].Rows[i].ItemArray[0].ToString();
                Response.Cookies.Add(coo);
            }
            catch (Exception ex)
            {
                Response.Write(ex.Message);
            }
        }

Answer 1

You are using the loop variable to acess the rows in the DataTable here:

coo["sogtit"] = ds.Tables["title"].Rows[i].ItemArray[0].ToString();

But the variable is initialized from the min and max ID values of your song_id .

I don't know why you need these values at all, why don't you loop the DataRows :

foreach(DataRow row in ds.Tables["title"].Rows)
{
    // ...
    int songID = row.Field<int>("song_id")
    Hyperlink hl = new HyperLink(); // you don't need the array of hyperlinks neither
    hl.ID = "hyperlink" + songID;
    string title = row.Field<string>("title);
    hl.Text = title;
    coo["sogtit"] = title;
    Panel1.Controls.Add(hl);
    // ...
}

Update

i want to access those latest upload song so i use for loop and index as min and max values. i mean want to access latest uploaded minimum 6 song

You could use Linq to get the last 6 uploaded songs:

var last6Uploaded = ds.Tables["title"].AsEnumerable()
    .OrderByDescending(r => r.Field<int>("song_id"))
    .Take(6);

foreach(DataRow row in last6Uploaded)
{
    // ...
}

Note that you should use a DateTime field instead of the primary-key.

Answer 2

The array index ( i ) and the value of song_id should have nothing to do with each other. What if your song_id started at 1000? Or if your database indexed by song_id in descending order?