ASP.NET reading data from DB

Question

new problem out there. While reading data from database and when it runs out of records, it simply says "Invalid attempt to read when no data is present", so the question is how to prevent that?

Here's my code:

{
    Label3.Text = Request.QueryString["Username"];

}

SqlConnection con = new SqlConnection("Data Source=JEVGENIJ-PC;Initial Catalog=ViaFitness;Integrated Security=True");
static SqlDataReader dr;
SqlCommand cmd;

protected void Button1_Click(object sender, EventArgs e)
{

    con.Open();

    SqlCommand cmd = new SqlCommand("select * from Summary where UserName='"+Label3.Text+ "'", con);

    dr = cmd.ExecuteReader();
    dr.Read();
    Label3.Text = dr[2].ToString();
    Label1.Text = dr[1].ToString();
    Label2.Text = dr[0].ToString();

}
 protected void Button2_Click(object sender, EventArgs e)
{
    dr.Read();
    Label3.Text = dr[2].ToString();
    Label1.Text = dr[1].ToString();
    Label2.Text = dr[0].ToString();
    con.Close();
}

}

MatthewMartin · Accepted Answer · 2013-04-21 13:33:47Z

2

You should make sure you have data in your reader:

protected void Button1_Click(object sender, EventArgs e)
{

    con.Open();

    SqlCommand cmd = new SqlCommand("select * from Summary where UserName='"+Label3.Text+ "'", con);

    dr = cmd.ExecuteReader();
    if (dr.Read())
    {
        Label3.Text = dr[2].ToString();
        Label1.Text = dr[1].ToString();
        Label2.Text = dr[0].ToString();
    }

}
 protected void Button2_Click(object sender, EventArgs e)
{
    if (dr.Read())
    {
        Label3.Text = dr[2].ToString();
        Label1.Text = dr[1].ToString();
        Label2.Text = dr[0].ToString();
    }
    con.Close();
}

Check out the MSDN-page for more info: http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldatareader.read.aspx

edited Apr 21, 2013 at 13:33

MatthewMartin

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answered Apr 21, 2013 at 13:31

Kenneth

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Comments

marc_s · Accepted Answer · 2013-04-21 16:11:55Z

2

call dr.read before every fetch. check if it is true , which means data is present

MSDN SqlDataReader.Read Method - Advances the SqlDataReader to the next record.

SqlDataReader reader = command.ExecuteReader();

// Call Read before accessing data. 
while (reader.Read())
{
        ReadSingleRow((IDataRecord)reader);
}

// Call Close when done reading.
reader.Close();

edited Apr 21, 2013 at 16:11

marc_s

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answered Apr 21, 2013 at 13:30

aked

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Comments

Kirill Bestemyanov · Accepted Answer · 2013-04-21 13:32:15Z

1

Datareader Read() method returns bool value. If it returns true, it succsesfully read next record, if it returns false - it is not read record because there is no more. So you should test result of Read method and then try to access to its values.

answered Apr 21, 2013 at 13:32

Kirill Bestemyanov

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Comments

mburm · Accepted Answer · 2013-04-21 13:32:21Z

0

Read() jumps to the next record. Is there nothing you cant' acces this. Try this for only one record

If(dr.Read()) {
    Label3.Text = dr[2].ToString();
    Label1.Text = dr[1].ToString();
    Label2.Text = dr[0].ToString();
}

or this for all

While(dr.Read())) {
    ' do something
}

answered Apr 21, 2013 at 13:32

mburm

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