More fun and games with Asp.net

23 Mar 2006

,

Starting to find my way around Asp.Net

I’m setting up a form for “forgotten password”. This is standard enough – give us your email address and we email you your password for the site.

This form has a single-line text input field (enter your email address here) and one button (Send Password). I want the button’s onsubmit event to be fired when if the user types in their email address and then (reasonably enough) presses the Enter key instead of groping for the mouse and clicking the big Send button. Works fine in Firefox, but not in IE. The form posts back, but I don’t get the OnSubmit event

Fix (and an excellent explanation) from the invaluable 4 Guys Obviously enough, I need to add another textbox – and since I don’t want another textbox I’ll make it invisible.

<asp:TextBox runat="server" style="visibility:hidden;display:none;" />

page_load doesn’t fire

22 Mar 2006

,

The Page_Load event in one of my pages was not firing – I eventually tracked this down to the InitializeComponent function (inside the “Web Form Designer generated code” block) The following line, which should have been automatically generated, was missing :

this.Load += new System.EventHandler(this.Page_Load);

The trouble is that I tend to stay away from the design view and work almost exclusively in the HTML view. And in making a new page, based on an existing one, this vital line was omitted. Much frustration.

It should be a simple query

3 Mar 2006

Get a list of users and the most recent training course they have attended. This should be a very simple query with a sub-select, but I’m using MySQL 3.23 and sub-selects are not available, so queries have to be rewritten using joins. (Sub-selects are available from MySQL 3.24 onwards). Took me a while:

select
   t1.*
from
   usertraining as t1
   left join usertraining as t2
   on t1.user_id = t2.user_id and t1.training_date<t2.training_date
where
   t2.training_date is null

This matches up the training courses. When the date is at its maximum (ie. the most recent) there are no matching dates in the joined table which are greater than that – so the t2 entries for that row are Null – and we use the where clause to pick out exactly those rows.
Another way to do it:

select
   t1.*
from
   usertraining as t1
   left join usertraining as t2
   on t1.user_id = t2.user_id
group by
   t1.training_date having t1.training_date = MAX(t2.training_date)
where
   t2.training_date is null

And of course, to get the user details is then very simple:

select
    users.*, usertraining.*
from
   users left join
   usertraining as t1 ON users.user_id = t1.user_id
   left join usertraining as t2
   on t1.user_id = t2.user_id and t1.training_date
where
   t2.training_date is null

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