How to properly use Session Parameters in asp.net

Question

I am not even sure how SessionParameters are meant to be used as opposed to a normal Parameters. What I am trying to do is Update or Insert records into my database based on a value from a Session variable "StaffID", which I know exists (based on debugging the PageLoad event). As it turns out my "StaffID" session is actually NULL (found after exhaustive debugging) and I get exceptions about trying to update a table with null values.

My SqlDataSource is thus ...

 <asp:SqlDataSource ID="SqlDataProgmDetails" runat="server" ConnectionString="<%$ ConnectionStrings:ATCNTV1ConnectionString %>"
                    UpdateCommand="UPDATE tblStudentProgramReg SET StaffModified = @StaffModified, DateModified = GETDATE() WHERE (ProgramEnrolmentID = @ProgramEnrolmentID)">
                    <UpdateParameters>
                        <asp:Parameter Name="EnrolmentDate" Type="DateTime" />
                        <asp:Parameter Name="StudentProgramNotes" Type="String" />
                        <asp:Parameter Name="TerminationDate" Type="DateTime" />
                        <asp:Parameter Name="StudProgEnrolStatusID" />
                        <asp:Parameter Name="QualificationCode" />
                        <asp:ControlParameter ControlID="gvPrograms" Name="ProgramEnrolmentID" Type="Int32" PropertyName="SelectedValue" />
                        <asp:SessionParameter Name="StaffModified" SessionField="StaffID" />
                    </UpdateParameters>
rs>
                </asp:SqlDataSource>

When I UPDATE my DetailsView I get the dreaded "String or binary data would be truncated. The statement has been terminated." error.

I know this is happening because the "StaffID" session variable that I am sure existed at one point is NULL in the UPDATE phase of the above SqlDataSource.

The only way around it I found was to force load the value in CodeBehind ...

protected void SqlDataProgmDetails_Updating(object sender, SqlDataSourceCommandEventArgs e)
{
    if (Session["StaffID"] != null)
    {
        e.Command.Parameters[5].Value = Session["StaffID"].ToString().Trim();
    }
}

protected void SqlDataProgmDetails_Inserting1(object sender, SqlDataSourceCommandEventArgs e)
{
    if (Session["StaffID"] != null)
    {
        e.Command.Parameters[8].Value = Session["StaffID"].ToString().Trim();
    }
}

But why should I have to do this?

I would have thought the StaffID should have loaded automatically as per the SessionParameter request in my ASP page.

Like I said, I am not sure how SessionParameters (or Session variables work) in general, so if someone could please explain why I have to use codebehind to get this to work, that would be appreciated?

Thank you

Elad Lachmi · Accepted Answer · 2014-05-13 06:42:58Z

1

The Session object is in fact an IDictionary<string, object>, which is persisted for you. It is persisted per-session. When a new session begins, the client receives a cookie from the server with a unique session identifier.

On each subsequent request the client sends the cookie to the server and in the global.asax the Session dictionary is repopulated. So let's say that in a code-behind you do Session[UserId] when the user authenticates, on each subsequent request you could do var UserId = Session[UserId] and as long as the session is "alive", you will receive the value you stored.

Restoring values from session as you have done is very logical. Since HTTP is state-less, Session is one of the mechanisms for simulating statefulness.

answered May 13, 2014 at 6:42

Elad Lachmi

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3 Comments

Fandango68 Over a year ago

Thanks Elad. So what you're saying is that restoring my session variable as I did above in code-behind is actually the only way to go, hence it's logical and acceptable?

Elad Lachmi Over a year ago

Yes, this usage is a big part of the WebForms story. This is exactly what session was designed for.

Fandango68 Over a year ago

Thanks Elad. Your answer is it then.

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