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Hi!

I would like to know where exceptions should be caught in a web project. I added an e-mail address Validation Rule to an entity. Now, if I enter an invalid e-mail address, I'm getting an error page with the following on it:

Unhandled Execution Error

Line 826:			
Line 827:			if (!entity.IsValid)
Line 828:				throw new Entities.EntityNotValidException(entity, "Update", entity.Error);
Line 829:			

Line 830:			TransactionManager transactionManager = null; 

Cheers!

JF 

Hi Phil!

That is exactly what I am doing. However, I still want to be able to display the message in a nice format, should an error arise. So the question remains, where should I catch the exception in order to be able to display the message in a nice or custom format?

Cheers!

JF

I'll assume this exception is being thrown from a provider's Update() method. I would recommend wrapping those types of calls in try/catch.  How specifically to handle it in your application depends how you have implmented it.  The simplest example is if you were calling the providers Update() method from within a button clicked event.  You would catch the EntityNotValidException and handle it appropriately. Note that you could get other types of exceptions such as SqlException due to database related problems (database timeout, database became unavilable, PK, FK or UK constriant errors).  The EntityNotValidException has a reference to the offending entity and a message.

This comes down to basic exception handling.  Do you know where the exception is being thrown from? Is there offending code that could be fixed? Can you catch and recover from the exception?  Should you wrap the exception inside another exception type and rethrow? Should catch and swallow the exception?  Swallowing exceptions should used only for specifically designed sitiations and should be clearly documented in code why the exception is being swallowed.

Here are a reference for you to read (non-NetTiers related):

Framework Patterns: Exception Handling, Logging, and Tracing 

What I did is I whipped up a few custom methods in the FormUtil class that catches these and displays them within a control on my masterpage.

If you use a gridView, you can catch them in the RowUpdated, RowDeleted, etc events.
If you use a formView, you can catch them in the ItemUpdated, ItemInserted, etc events.
Or you can just use the Deleted, Insrted, Updated events on the datasource.

I prefer catching them in a gridView/formView -vs- the datasource directly so you can set the KeepInInsertMode/KeepInEditMode flags.  This way the data entered stays (errors and all) and a nice error message is displayed.

Here is a sample one that I use for formview Updates:

public static void handleUpdate(FormView formView, String redirecturl)

{

if (formView != null)

{

formView.ItemUpdated += new FormViewUpdatedEventHandler

(

delegate(object sender, FormViewUpdatedEventArgs e)

{

if (e.Exception != null)

{

logException(e.Exception);

displayMasterError(e.Exception, formView.Page);

e.ExceptionHandled = true;

e.KeepInEditMode = true;

}

else

{

if (!String.IsNullOrEmpty(redirecturl))

{

string url = String.Format(redirecturl, ((formView.SelectedValue == null) ? null : formView.SelectedValue));

HttpContext.Current.Response.Redirect(url);

}

}

}

);

}

 

}

Anyhow I'm too lazy to tidy that up so it doesn't take so much freakin space.   Community server sure looks pretty but....  Anyhow I digress.

logException is a custom method that calls the enterprise exception handler.
displaymastererror is a custom method that finds the error control within the masterpage and stuffs the error message in it/toggles visibility.

This will (optionally) automatically redirect after a successfull update.

Hi Meech,

This is cool. What about submitting all of your methods to be added to the standard FormUtil?

Cheers

swin

Hi!

Thanks for all that input! As I can see, there is no single best practice method.

Phil: Merci pour le lien! I'll have a look at the article. About my application: I'm not calling Update*( from within a button clicked event. I'm using buttons like these ones in VormViews:

<asp:Button ID="SaveButton" runat="server" CausesValidation="True" CommandName="Update" Text="Sauvegarder"/>

<asp:Button ID="CancelButton" runat="server" CausesValidation="False" CommandName="Cancel" Text="Annuler"/>

Using the FormView DataSource and the button CommandName, the application automatically "knows" what to do with the entity.

Yes, I know where the offending code comes from. I made this error occur on purpose. I added a Validator to my entity, and then I entered invalid data through the FormView in order to test the new validator. The error message is not the problem. My problem is more about what is the best practice to have these error messages appear within the application on a form that I designed. Right now, it is appearing on the standard ASP.NET error page.

I will try Meech's solution, although it seems to be a lot of work to add all that code on every form. I was hopping ASP.NET 2.0 and .netTiers would have a simpler mechanisme for this (read with less code).

Cheers!

JF

I don't put that in every page, i put those in the FormUtil class.

Then on every page, I put something like:

protected void Page_Load(object sender, EventArgs e)
    {
        FormUtil.handleSelect(HotListsDataSource);
        FormUtil.handleUpdate(GridView1);
        FormUtil.handleInsert(FormView1);
        FormUtil.handleDelete(GridView1);
    }

I've attached a text file that contains most of my Formutil extensions.  It has all the handlexxxx that I use and a few helper functions.  You'll have to modify it to work in your particular scenario (exceptionpolicy name, master page control namse, etc)...

Hi Meech,

Thanks for this!

Cheers

swin

Hi Meech!

I added your code to my project and it is working beautifully. Delegates are new to me, but they seem to simplify the task quite a bit. Your solution requires less code than I thought initially.

Cheers!

JF

P.S. To display error messages, I used the ASP.NET Pop-up Control presented here: http://www.codeproject.com/aspnet/asppopup.asp. I find it quite interesting. 

How do I must configure the entlib.config to use this method?

postHandlingAction="NotifyRethrow" ??? "None"? "ThrowNewException" ??

 Thanks,

RAUL DUQUE
Bogotá, Colombia

Hola Raul!

On my project, I'm using postHandlingAction="NotifyRethrow".

Here is the whole section from my entlib.config:

    <exceptionHandling>

        <exceptionPolicies>

            <add name="NoneExceptionPolicy">

                <exceptionTypes>

                    <add type="System.Exception, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"

                        postHandlingAction="NotifyRethrow" name="Exception">

                        <exceptionHandlers>

                            <add logCategory="Exceptions" eventId="100" severity="Error"

                                title="Mammouth Exception Handling" formatterType="Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.XmlExceptionFormatter, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling, Version=2.0.0.0, Culture=neutral, PublicKeyToken=null"

                                priority="0" type="Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Logging.LoggingExceptionHandler, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Logging, Version=2.0.0.0, Culture=neutral, PublicKeyToken=null"

                                name="Logging Handler" />

                        </exceptionHandlers>

                    </add>

                </exceptionTypes>

            </add>

        </exceptionPolicies>

    </exceptionHandling>

I hope this helps!

JF