[RESOLVED] Exception Issue and N-tier issue (c#)

[zero cool]

Hi,

I was required to build a N-tier system.

User -> Business -> Data -> Database
Interface <- layer <- Access <-

My question is, how do u implement the exception in the data-access-layer and show it to the user-interface layer.

The following is my code from the data-access layer in c#

public class DataAccess
{
   public string ReadData()
   {
      try
      {
         // Read data from the database
      } 
      catch (Exception e)
      {
         throw new IOException ("Could not read from database", e);
         /* I can just retun null here, but I just want to show the message to 
             the user            
         */
      }
   }
}

Thanks a lot.

[zero cool]

User -> Business -> Data -> Database
Interface <- layer <- Access <-

They should be

User Interface <-> Business layer <-> Data access <-> Database

[Sgt-Peppa]

In your Data Access Class just throw your exception. Like this:

catch (Exception e)
{
 throw new IOException ("Could not read from database. Details: " + e.Message, e);
}

In your BusinessLayer you catch Exceptions again and throw it again:

catch IOException(Exception e)
{
 throw new Exception ("Error in my Class-myFunction. Details:" + e.Message, e);
}

And in your User Interface catch the error again and display the Information you want to show the user. Since you always including the original Exception in your new Exceptions you have control over the whole Stack Trace. Bubbling your Exception all the way up to your user-interface makes sense since all of your other layers dont know what Information you actually want to present.
In your User-Interface layer you can then format your Exception nicely and present the Error Information you want.

Of course catching Exceptions is expensive in .NET but still I like this Method the most!

HTH,

Stephan

[Sgt-Peppa]

Oh and by the way, I usually create my Own Exceptions for a lot of classes I use. For example my Own DataAccessException. So if an error occures in my Data Access Class I catch that and throw a new DataAccessException. In my BusinessLayer I can then watch for that specific Exception and handle it accordingly. For example retry, or similar!

Stephan

[zero cool]

To Stephan,

Just wondering how can u catch the exception in the user-interface ???

Thanks a lot. I am so virgin to this programming

[Sgt-Peppa]

OK this is just a quick and dirty example. Havnt tested this:

In your DataLayer do something like this:

public static string doSomething
{
	int b = 10;
	int c = 0;
	try
	{
		/* Divide by Zero to force an Exception */	
		int a = b /c;
		return a.ToString();
	}
	catch(Exception ex)
	{
		throw new Exception("Error in blah" + ex.Message,ex); 
	}
}

This method will throw an Exception.
In your Business Layer oyu call the Method and catch an Exception like this:

public static string doSomething()
{
    try
    {
    	return DataLayer.doSoemthing();    
    }
    catch(Exception ex)
    {
    	throw new Exception("Error in blah" + ex.Message,ex);
    }
}

And finally in your UserInterface do something like this:

try
{
	txtMyResult = BusinessLayer.doSomething();
}
catch(Exception ex)
{
	txtMyResult = ex.Message;
}

Again this is just some quick and dirty example. And it might be a good idea to create your own Exception classes. You are more variable in your Error handling then. If you have any more questions just post!

Stephan

[zero cool]

Cheers Stephan,

You're a legend.

[zero cool]

Ehm.. Stephan

Do u mind posting some coding of yours in your own exception class ?? Sorry, for being such a pain....

[Sgt-Peppa]

Thsi is a good reading for Exceptions. I'll post some code tomorrow! Not at work Today!

Edit forgot the link:

Exception Handling

[zero cool]

Hi Stephan,

Thanks for the link
I am an exception-master to be after reading them


cheers