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Managing an invalid cast exception


I have built a web application that will be a very high profile application.
We had tested it, demonstrated it and shown that it all works.

On a dress rehearsal run through, it failed spectacularly. I was so
embarrassed and felt like killing the person that made it fail. However,
when it goes live, IT MUST NOT FAIL.

The system has a backoffice system that takes an excel spreadsheet from the
client and uploads it to the webserver. I suppose part of the original issue
was lack of knowledge of excel. However, what I then do is open the
spreadsheet and save the contents into SQL Server, the results being
delivered from SQL to the website.

The front end displays the results. I am using various controls, such as
datagrids, datalists and even labels. Many of the datagrids/datalists etc
are not autogenerating. I use container.datai tem to display the results, in
most cases.

The issue arose when we started uploading data in excel. During development
and test, the data in excel was probably being entered in rows, one after
the other. However, during dress rehearsal, the rows are being entered
randomly. Some of you may be aware (as I am now) that excel doesn't
initially care or even know what datatype is in a particular column, so if
you have mixed numbers and words in the same column, depending what goes off
in the first few rows of that column defines what the column data type is.
This appears to override what the column format has been specifically set

The result was that say the first 5 rows had numbers, the sixth row was text
(with the whole column being defined as text), upload, drop direct into a
datagrid or copy to database (database being defined as nvarchar for this
field) the sixth row would then be null. (This was showing even by dropping
the excel data direct into the datagrid)

This absolutely caught me out. I was forced to accept responsibility even
though it was not my fault. :-(

Anyhow, now I have explained the situation, I have 2 questions.
1. In the ASP.NET page, I am using <%# DataBinder.Eval (Container.Data Item,
"WinningDetail" ) %> in an item template of a datagrid, which I have already
bound to.

Now, with the data coming out of the database being null, I had an invalid
cast exception. How can I protect against that. I would rather fail
gracefully so that I can try and fix it (I will be in the back office during
the critical period) than to have it throw the yellow error screen. I can't
write fixes for every possibility, so I need something like a try/catch but
inside the aspx.

2. This question is quite open ended but is about testing. Given my scenario
above, how could/should I have tested in order that it wouldn't have failed?

Thanks for your time.

Best regards,
Dave Colliver.
http://www.FOCUSPortals.com - Portal Franchises available

Nov 19 '05 #1
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