c# - ASP.NET malfunction when signing up to an event -

we 2 students trying develop website asp.net functions. have come issue:

we have booking page logged in user can sign events, have made separate tabel handling sign ups.

in table have member_id session, , event id.

we continue check member_id , event_id in database make sure same member cant sign same event twice.

protected void page_load(object sender, eventargs e) {     if (session["medlems_id"] == null)          response.redirect("medlemslogin.aspx");     if (!ispostback)     {         if (session["redirectedmessage"] != null)         {             lblmessage.text = session["redirectedmessage"].tostring();             session["redirectedmessage"] = null;         }     } }  protected void gridview1_rowcommand(object sender, gridviewcommandeventargs e) {     // få fat hold_id fra den valgte kolonne og gem det variablen varhold_id     var varhold_id = gridview1.rows[convert.toint32(e.commandargument)].cells[6].text;      //db connection      string connstr = @"provider=microsoft.ace.oledb.12.0;data source=|datadirectory|\drt.mdb;jet oledb:database password=password";     oledbconnection myconn = new oledbconnection(connstr);      myconn.open();      oledbcommand cmd = new oledbcommand(strcmd, myconn);      cmd.commandtext = "select * booking hold_id = @hold_idpar";     cmd.parameters.addwithvalue("hold_idpar", varhold_id);      oledbdatareader objreader = cmd.executereader();      if (objreader.read())     {         var antalpladser = convert.toint32(objreader["pladser"]);         var antaltilmeldte = convert.toint32(objreader["tilmeldte"]);         var holdnavn = convert.tostring(objreader["hold"]);         var medlems_idva = session["medlems_id"];            if (antalpladser > 0)         {               oledbcommand dbcmd = new oledbcommand(strcmd, myconn);             dbcmd.commandtext = "select hold_id tilmelding hold_id = @hold_idpar , medlems_id = @medlems_idpar";             dbcmd.parameters.addwithvalue("medlems_idpar", medlems_idva);             dbcmd.parameters.addwithvalue("hold_idpar", varhold_id);                oledbdatareader valreader = dbcmd.executereader();             if (valreader.read())             {                 lblmessage.text= "du er allerede tilmeldt";             }              else {             oledbcommand cmd3 = new oledbcommand(strcmd, myconn);             cmd3.commandtext = "update booking set tilmeldte = tilmeldte+1, pladser = pladser-1 hold_id = @hold_idpar";             cmd3.parameters.addwithvalue("hold_idpar", varhold_id);             cmd3.executenonquery();              oledbcommand cmd2 = new oledbcommand(strcmd, myconn);             cmd2.commandtext = "insert tilmelding (medlems_id, hold_id) values (@medlems_idpar, @hold_idpar)";             cmd2.parameters.addwithvalue("medlems_idpar", medlems_idva);             cmd2.parameters.addwithvalue("hold_idpar", varhold_id);             cmd2.executenonquery();                session["redirectedmessage"] = "du er tilmeldt holdet" + holdnavn;             response.redirect("kalender.aspx");             }             //response.redirect("kalender.aspx");         }         else         {             lblmessage.text = "der er ikke flere pladser";         }     }     objreader.close();     myconn.close(); }  private object int32(object p) {     throw new notimplementedexception(); }   public string strcmd { get; set; } 

our problem that, members can keep signing events. if event id , member id same, works correctly reason.

here translation database since used danish words naming db.

    hold_id=event_id      medlems_id=member_id 

hope can us, since our hair becoming quite gray.

before insert can use below query:

select event_table.event_id event_table inner join member_table on event_table.event_id=member_table.event_id  

and not sign member if event_id selected above query matches event id in session. (suppose table containing events 'event_table' , table containing member sign 'member_table')