SqlCommand.ExecuteReader and getting past the first row

Question

I'm fairly new to ASP.NET and as a self-chosen assignment I am to create a simple blog. It's very nearly finished, but I've run into a problem. As you can see from the code I am first using a query to return the amount of blog entries from my SQL server database. A for loop then reads titles, dates and text content from all the rows and creates a html div which it loads them into. Works great except for one thing: ExecuteScalar() only reads the first row, which will return the same value for each iteration causing all the blog entries to be the same.

I need a way for the reader to move on with each iteration. I've considered making a SQLbulkcopy into another table which I can then delete the top row from in the for loop, but this seems like it would slow down the page a fair amount if it's to be done on each Page_Load.

string SQLreadTitle = "Select BLOG.BlogTitle from BLOG order by BlogID DESC";
string SQLreadDate = "Select BLOG.BlogDate from BLOG order by BlogID DESC";
string SQLreadText = "Select BLOG.BlogText from BLOG order by BlogID DESC";
string SQLcountIDs = "Select count(BlogID) from BLOG";

protected void Page_Load(object sender, EventArgs e)
{

    int i;
    SqlConnection con = new SqlConnection(cnString);
    con.Open();

    SqlCommand countIDs = new SqlCommand(SQLcountIDs, con);
    int count = Convert.ToInt32(countIDs.ExecuteScalar());



    for (i = 0; i < count; i++)
    {
        SqlCommand readTitle = new SqlCommand(SQLreadTitle, con);
        string titleString = readTitle.ExecuteScalar().ToString();
        SqlCommand readDate = new SqlCommand(SQLreadDate, con);
        string dateString = readDate.ExecuteScalar().ToString();
        SqlCommand readText = new SqlCommand(SQLreadText, con);
        string textString = readText.ExecuteScalar().ToString();



        System.Web.UI.HtmlControls.HtmlGenericControl dynDiv =
        new System.Web.UI.HtmlControls.HtmlGenericControl("DIV");
        dynDiv.ID = "BlogPost";
        dynDiv.InnerHtml = "<div id=\"BlogTitle\">" + 
            titleString + "</div><br /><div id=\"BlogDate\">"
            + dateString + "</div><br /><br /><div id=\"BlogText\">" 
            + textString + "</div>";
        Label1.Controls.Add(dynDiv);


    }
    con.Close();
}

Thanks in advance!

So why don't you use `ExecuteReader()`? – SLaks Mar 25 '12 at 23:38 — SLaks, Mar 25 '12 at 23:38

score 5 · Accepted Answer · answered Mar 25 '12 at 23:43

You are making life far too hard on yourself. You should have a single select statement then read each of the rows that is returned.

    string SQL = "Select BLOG.BlogTitle, BLOG.BlogDate, BLOG.BlogText from BLOG order by BlogID DESC";
    // Positions of the columns you are reading
    const int TITLE_ORDINAL = 0;
    const int DATE_ORDINAL = 1;
    const int TEXT_ORDINAL = 2;

    protected void Page_Load(object sender, EventArgs e)
    {
        using (var con = new SqlConnection(cnString))
        {
            con.Open();
            try
            {
                using (var oCommand = new SqlCommand(SQL, con))
                {
                    using (var oReader = oCommand.ExecuteReader())
                    {
                        while (oReader.Read())
                        {
                            var dynDiv = new System.Web.UI.HtmlControls.HtmlGenericControl("DIV");
                            dynDiv.ID = "BlogPost";
                            dynDiv.InnerHtml = "<div id=\"BlogTitle\">" +
                                oReader.GetString(TITLE_ORDINAL) + "</div><br /><div id=\"BlogDate\">"
                                + oReader.GetString(DATE_ORDINAL) + "</div><br /><br /><div id=\"BlogText\">"
                                + oReader.GetString(TEXT_ORDINAL) + "</div>";
                            Label1.Controls.Add(dynDiv);
                        }
                    }
                }
            } finally {
                con.Close();
            }
        }
    }

Thank you! Being a newbie I thought I was going the right way but I can clearly see your methods are much better. I've learned some things I didn't know you could do thanks to you and now my blog is finished. Had to change oReader.GetString(DATE_ORDINAL) to GetDateTime, but otherwise it worked perfectly. Now I'll just have to study the code. Thanks again :) — Siken, Mar 26 '12 at 00:03

Claudio Redi · Answer 2 · 2012-03-25T23:55:18.717

I think you have read a little more about ADO.NET since you have some wrong concepts. SqlCommand.ExecuteScalar is used to get a single value from database, not to get a set of data.

You don't need to get the item count to iterate over a record set. Using SqlCommand.ExecuteReader you could get all the data you need in a single query. Here you have a sample code that you can follow

string sqlQuery = "Select * from BLOG order by BlogID DESC";
using (SqlConnection con = new SqlConnection(cnString))
{
    con.Open();
    using (SqlCommand cmd = new SqlCommand(sqlQuery, con))
    {
        using (SqlDataReader dr = cmd.ExecuteReader())
        {
            while (dr.Read())
            {
                System.Web.UI.HtmlControls.HtmlGenericControl dynDiv =
                new System.Web.UI.HtmlControls.HtmlGenericControl("DIV");
                dynDiv.ID = "BlogPost";
                dynDiv.InnerHtml = "<div id=\"BlogTitle\">" +
                    dr["BlogTitle"] + "</div><br /><div id=\"BlogDate\">"
                    + dr["BlogDate"].ToString() + "</div><br /><br /><div id=\"BlogText\">"
                    + dr["BlogText"] + "</div>";
                Label1.Controls.Add(dynDiv);
            }
        }
    }
}

Here you have an MSDN article that may help you to understand how to use a SqlDataReader

Thank you, I'll be sure to read up on ADO.NET and how Executereader works! — Siken, Mar 26 '12 at 00:07

score 0 · Answer 3 · answered Mar 25 '12 at 23:43

ExecuteScalar isn't what you need here, and you don't need the count either. Read here about data adapter. afterr the Fill method call, thr data table has all the content from the db and can be iterated through. You can read about the data table class here.

A simple iteration example would be:

DataTable tbl = new DataTable();

foreach (DataRow row in tbl.Rows)
{
    foreach (DataColumn col in tbl.Columns)
    {
        object cellData = row[col];
    }
}

SqlCommand.ExecuteReader and getting past the first row

3 Answers3