Find the value in gridview using findcontrol and comapre it with data in database

Question

 protected void LinkButton_Click(Object sender, EventArgs e)
    {
        String MyConnection2 = "Server=localhost;database=ovs;Uid=root;password=; Convert Zero Datetime=True";
        DateTime time = DateTime.Now;              // Use current time
        string format = "yyyy-MM-dd HH:mm:ss";
        string UserName4 = HttpContext.Current.User.Identity.Name;
        GridViewRow grdrow = (GridViewRow)((LinkButton)sender).NamingContainer;
        Label lblStudentId = (Label)grdrow.Cells[0].FindControl("lblID");
        string studentId = lblStudentId.Text;
        String query = "insert into voting (CandidateStudentID,voterStudentID,DateTime)values ('" + lblStudentId.Text + "','" + Session["UserName"].ToString() + "','" + time.ToString(format) + "')";
        foreach (GridViewRow row in GridView2.Rows)
        {
            Label lblVoter = row.FindControl("lblVoter") as Label;
            string voterID = lblVoter.Text;


            if (Session["UserName"].ToString().Equals(lblVoter.Text))
            {
                Label1.Text = "You voted before";

            }

        }
        MySqlConnection MyConn2 = new MySqlConnection(MyConnection2);
        MySqlCommand MyCommand2 = new MySqlCommand(query, MyConn2);
        MySqlDataReader MyReader2;
        MyConn2.Open();
        MyReader2 = MyCommand2.ExecuteReader();
        Label2.Text = "Thank you for You Vote";

    }


  <asp:GridView ID="GridView2" runat="server"  AutoGenerateColumns="False" Font-Size="Medium">
          <Columns>
          <asp:TemplateField HeaderText="Student ID">
  <ItemTemplate>
     <asp:Label ID="lblVoter" runat="server"   Width="150px"  Text='<%#Eval("voterStudentID") %>'/>
 </ItemTemplate>
 </asp:TemplateField>
              
          </Columns>
       </asp:GridView>


 protected void loadCandidate()
    {
        con.Open();
        MySqlCommand cmd = new MySqlCommand("select studentID ,name from candidate  ", con);
        MySqlDataReader dr = cmd.ExecuteReader();
        if (dr.HasRows == true)
        {
            GridView1.DataSource = dr;
            GridView1.DataBind();
            con.Close();

            con.Open();
            MySqlCommand cmd2 = new MySqlCommand("select voterStudentID from voting  ", con);
            MySqlDataReader dr2 = cmd2.ExecuteReader();

            GridView2.DataSource = dr2;
            GridView2.DataBind();
        }
    }

StudentID display in gridview2

I want to prevent duplicate voting in the database. Now I'm facing a problem which when the user login as first users in the StudentID table which is 1909404, when the 1909404 already exist in the database, It will display the error message. But when the user's login as the second user in the StudentID table which is 1909362, even though the user ID already exists, It will no show the error message. I would like to show the error message as long as the user ID existed in the database (which mean they voted before).

Answer 1

Change it like this....

foreach (GridViewRow row in GridView2.Rows) {
  Label lblVoter = row.FindControl("lblVoter") as Label;
  if (Session["UserName"].ToString().Equals(lblVoter.Text)) {
    Label1.Text = "You voted before";
    return;
  }
}
// Since we looped through all the rows and did NOT find a match...
// Then they can vote 
MySqlConnection MyConn2 = new MySqlConnection(MyConnection2);
MySqlCommand MyCommand2 = new MySqlCommand(query, MyConn2);
MySqlDataReader MyReader2;
MyConn2.Open();
MyReader2 = MyCommand2.ExecuteReader();
Label2.Text = "Thank you for You Vote";