Re: New to VB.NET...HELP REQUIRED IMMEDIATELY
From: W.G. Ryan eMVP (WilliamRyan_at_gmail.com)
Date: 01/28/05
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Date: Fri, 28 Jan 2005 12:02:43 -0500
Scott - a DataReader requires an open and available connection and is only
valid in a 'live' context regarding the connection. You can't pass more
than one command over the same connection at one time - even if the command
has the exact same commandtext. The execution of the first command ins't
even finished yet when it's being called again on the same wire. So
technically, there aren't Two different command objects instantiated here,
but there are two commands attempting to be sent with the same connection -
which isn't going to work. You would certainly agree that through Query
Analyzer for instance, it's possible to exectue 2 commands right? Even
though in QA you aren't ever even explicity creating even one SqlCommand
object. Moreover, since the query is using an aggregate function to return
one single value - excecutescalar makes more sense in every regard 1) You
don't need the datareader object in the first place 2) you don't need to
extra code associated with iterating through it.
I do acknowledge that there aren't 2 SqlCommand objects - but my statement
that you're trying to fire two commands over the same connection isn't
incorrect.
--
W.G. Ryan, MVP
www.tibasolutions.com | www.devbuzz.com | www.knowdotnet.com
"Scott M." <s-mar@nospam.nospam> wrote in message
news:OGuq1LNBFHA.136@TK2MSFTNGP14.phx.gbl...
> I don't see him using one connection for 2 different commands. I see him
> calling ExecuteReader on the same command twice. There is only one
command
> object in his code.
>
>
> "W.G. Ryan eMVP" <WilliamRyan@gmail.com> wrote in message
> news:OnGYw1KBFHA.3576@TK2MSFTNGP11.phx.gbl...
> > Scott already answered the crux of your problem - you are using the same
> > connection for two different commands which you can't do until ADO.NET
2.0
> >
> > But since your first execution is MAX() - then you should probably opt
for
> > ExecuteScalar instead of Reader. If nothing else it will save you a few
> > lines of code and make your intent a little clearer.
> >
> > Also, you should consider using a Finally Block and closing your
> > connection
> > in the finally - that's the only way youy can make sure it will get
> > closed.
> >
> > And as always - I have to include my obligatory rant against catching
> > system.Exception here. Since your not doing anything with your
exception
> > other than writing it out - you probably ought to catch a OleDbException
> > for
> > the connection.Open and the Execute statements - if you got a
> > StackOverflow
> > or something else there - well you may want to respond differently.
But
> > that's another story.
> >
> > --
> > W.G. Ryan, MVP
> >
> > www.tibasolutions.com | www.devbuzz.com | www.knowdotnet.com
> > "santosh singh via DotNetMonster.com" <forum@DotNetMonster.com> wrote in
> > message news:09d9cc428c6e41a4b297c987ab109eac@DotNetMonster.com...
> >> Hi,
> >> I'm new to VB.NET..I'm developing a login page...im getting this
error..
> >>
> >> System.InvalidOperationException: ExecuteReader requires an open and
> > available Connection. The connection's current state is Open, Fetching.
at
> > System.Data.OleDb.OleDbCommand.ValidateConnectionAndTransaction(String
> > method, Int32& localState) at
> > System.Data.OleDb.OleDbCommand.ExecuteReaderInternal(CommandBehavior
> > behavior, String method) at
> > System.Data.OleDb.OleDbCommand.ExecuteReader(CommandBehavior behavior)
at
> > System.Data.OleDb.OleDbCommand.ExecuteReader() at
> > bt.index.Page_Load(Object
> > sender, EventArgs e) in d:\inetpub\wwwroot\bt\index.aspx.vb:line 56
> >>
> >>
> >> The code in .aspx.vb page is
> >>
> >>
> >> Private Sub Page_Load(ByVal sender As System.Object, ByVal e As
> > System.EventArgs) Handles MyBase.Load
> >> 'Put user code to initialize the page here
> >> If Not IsPostBack Then
> >> Try
> >>
> >>
> >>
> >> Dim MyConn As OleDbConnection = New
> > OleDbConnection(ConfigurationSettings.AppSettings("strConn"))
> >> Dim strVisitor As String
> >> Dim visitorCmd As OleDbCommand
> >> Dim vRdr As OleDbDataReader
> >> strVisitor = "select max(v_id) from visitor"
> >> visitorCmd = New OleDbCommand(strVisitor, MyConn)
> >> MyConn.Open()
> >> Dim old_visitor As Integer
> >> Dim new_visitor As Integer
> >>
> >> vRdr = visitorCmd.ExecuteReader()
> >> While vRdr.Read()
> >> If Not IsDBNull(visitorCmd.ExecuteReader()) Then
> >> old_visitor = vRdr.Item(0)
> >> End If
> >> End While
> >>
> >> new_visitor = old_visitor + 1
> >> lblvisitor.Text = new_visitor
> >> MyConn.Close()
> >>
> >> Catch ex As Exception
> >> Response.Write(ex)
> >> End Try
> >>
> >> End If
> >> End Sub
> >>
> >>
> >>
> >> Your help will be much appreciated
> >>
> >> --
> >> Message posted via http://www.dotnetmonster.com
> >
> >
>
>
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