Thanks for these tutorials.They sure are better than reading dozens of pages to get the same results.Beth explains quite well, too.

Talking about validation of table fields and business rules, you talk about the best practice of not putting validation at form level, but rather at the dataset level.Now, how about setting the constraints at database level, which could be even better for use across different applications.

For example, if you specify fields being "required" or use "validation rules" on an Access database, how would you handle those exceptions (constraint failures) elegantly in a VB 2008 form?

Are there any handy videos, tutorials or other references available on the MS site that deal with this?

Thanks.

Hi Ivan,

Validation rules should also be checked on the client application as well as enforced on the server for better performance. In order to check database constraint violations you'd have to handle the SqlException in your save routine. This means you're opening a connection to the database and this is expensive. If you know there are certian rules that should be checked before you head to the database, then you'll want to run those on the client. In this video I'm showing how to do that by adding validaiton code to the DataTable partial class.

Of course you'll also want to handle unexpected SqlExceptions as well. Concurrency violations for example. This is why you should make sure you handle any exceptions when you save changes. Here's an example: http://msdn.microsoft.com/en-us/library/y8fyz6xy.aspx

I'd also take a look at this article on designing a good exception handling strategy for your applications:
http://msdn.microsoft.com/en-us/magazine/cc164003.aspx

I don't have a video of this but I'll add it to the list. Thanks for the feedback! :-)

Cheers,
-B

Hi Beth,
I really appreciate the work you have put into these videos. They are a real help!
 
It is great that you talk about best practices when developing as well.
 
Following best practices I have implemented all my business rules in the dataset using the partial classes as you just as you have described in this video. I have a similar situation with the master table being a "Details View" and the detail table is in a DataGridView.
 
The issue that I have encountered is when you have a Business Rule implemented in the partial class that is the same as a constraint in the DataSet. For Example an AllowDBNull = False in a DataColumn and a Business Rule coded to check for Null on that same column.
 
In a "Details View" type data block you can override the BindingNavigator functions to not allow navigation, add, and save on your master BinidingSource until all the business rules are satisfied. I used the AddingNew Event on the detail BindingSource as you described in your video to do the EndEdit on the master. And I capture the PositionChanged event on the master to enable or disable the ability to add rows to the detail tables depending on the business rules on the master being satisfied.
 
The DataGridView is another story. In order to prevent the DataGridView from throwing its own DataError event I capture the RowValidating event. If the business rules have not been satisfied I cancel the event. I am having a multitude of problems with this approach. As I understand it is best practice to try to prevent the error than to trap the error. Trapping the error thrown by the DataGridView has been giving me trouble as well.
 
Are there some best practices around meshing the interface objects with the business rules built in the dataset?
 
If I relax the constraints in the dataset (i.e set AllowDBNull = True) my business rules fire fine and I don’t need to deal with all the errors thrown by the dataset and I can just prevent the save. I know this has got to be poor programming practice. It gave me a sick feeling inside anyway…
 
I have had one other problem. When the last row in a DataGridView is deleted the TableNewRow event fires twice in the DataSet and then all my NotNull type business rules fire causing the row to have errors. At that point I cannot save.
 
I hope I have presented this clearly. I was an Oracle developer for 11 years before moving to the “Goodness that is VB”.
 
I have posted on the MSDN forums and have not really got an answer that follows best practices.
 
Thanks!

Hi koby16,
 
What I try instead is set defaults on the columns that do not allow nulls (i.e. "", 0, False) in the TableNewRow handler and then check for these "empty" values in your validation routines. That way the constraints won't fail on the DataSet but you can still enforce validation.
 
HTH,
-Beth

Cool. Thanks Beth. I will give it a try.
 
I am having another problem with a TextBox bound to a DataTable Column that is a Decimal. When you type a non-numeric value in the TextBox I get an error icon with error text "Input string not in a correct format". Then you cannot leave the TextBox until you enter a value even though the data source allows nulls.
 
The problem is the validation is not getting to my business rules in the DataSet partial class. This seems to be an error returned from some other source.
 
Thanks Again!
Koby

Hi Beth,
I created a Form based on your Videos. They are really helpful! But now I have a problem with the Errorprovider.
I implemented a validation on a field which is not allowed to have duplicate number. If the number inserted is already existing I set the ErrorProvider to give a Message as you described in your video. So far so good. But now I try to use CancelEdit (on a BindingNavigator Button) so the Original Entry is back again. Unfortunately the Errormessage is still shown. I tried to use ErrorProvider.SetError(FNr,"") and ErrorProvider.Clear after the CancelEdit. This works until I navigate to the next Record. Whenever I return to the Record I had the Changes the ErrorProvider shows me the same Errormessage again everthough the OriginalEntry is shown.
Do you have an idea how I can handle this problem?
Thanks

I hope you understand my problem because my English is not very good.
Thanks a lot