Visual Basic

11-Mar-09 9:58

I have written a tcp server to handle requests, most of which access a database for some sort of information. My question is how do I structure the error handling. Some errors I want to propagate up to the user level and others I want to just handle where they are. For example. If the database in unreachable - I want to wait and then try again but if there is a problem with the retrieved data, I want to send it up to the calling code so I can Send a tcp message back to the client. I am not sure if I should be putting try catches in all my routines (which i dont think is right) or just in specific spots. I am just having trouble figuring out the correct way to do this.

Does anyone know of some good error handling tutorials I could take a look at?? Thank You

modified on Thursday, March 12, 2009 7:38 AM

Dave Kreskowiak12-Mar-09 3:46

Dave Kreskowiak

12-Mar-09 3:46

captainmogo wrote:
If the database in unreachable - I want to wait and then try again but if there is a problem with the retrieved data, I want to send it up to the calling code

This is where you'd throw your exception. The calling code would be running in a Try/Catch block to catch this error. It's the calling code that has to worry about what the problem is and how to deal with it, not the database code.

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Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008

captainmogo12-Mar-09 4:15

12-Mar-09 4:15

ok well my calling code is in a backgroundworker

Class1
Private Sub DoSomething(ByVal sender as Object, ByVal e as DoWorkEventArgs) Handles worker.DoWork

SetTriggerStatus(nam, id, "Started")

Query(start_time, end_time)

....Wait

Query(start_time, end_time)
End Sub
End Class

Module1
Sub SetTriggerStatus(Byval nam as String, ByVal id as Integer, ByVal status as String)
Dim connection as New Client.OracleConnection(My.Settings.OracConnectionString.ToString)
Dim cmd as Client.OracleCommand = Nothing

Try
cmd = New Clinet.OracleCommand("INSERT INTO StatusLog (Name, RuleID, Status) VALUES(:Name,
:RuleID,:Status)", connection)

....set oracleparameters
....execute script

connection.close

Finally
..dispose
End Try
End Sub
End Module

Basically if I get an error connecting to the database in here, I want it to try again. So I would have to put the try/catch around the SetTriggerStatus call from within DoWork? Same with both the query subs?) I also read somewhere that it is not good practice to be putting try/catch blocks in background workers (of course I cant find a good explanation for it now)

Luc Pattyn12-Mar-09 4:54

Luc Pattyn

12-Mar-09 4:54

Hi,

here are some guide lines, they should enable you to make good decisions about error handling:

1. only try-catch exceptions your catch can deal with; don't just swallow exceptions to make them go away; always leave some trace of an exception, say in a log file. it makes debugging much harder if you don't.

2. when you want retries, you can but the try-catch inside the loop and swallow exceptions in all but the last iteration. Don't retry forever.

3. background threads typically need to report back to their parent thread, whether success or failure. You shouldn't have a background thread retry forever, or just fail or give up without telling.

4. when your app needs to report failure back to the user, make sure to have both a message the user can understand (and knows what we'd do best then), and the technical information behind it (that could be the low-level exception) should be somewhere, again in a log file.

Smile | :)

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captainmogo12-Mar-09 5:03

12-Mar-09 5:03

I am going to write the errors to a log file because there is not user interface for this app. It is actually going execute on a machine with no monitor. The requirements I was given was to have the the db queries fail on any error but I want to try and handle what I can before saying its failed. say somethign like the db is not available.

Luc Pattyn wrote:
. when you want retries, you can but the try-catch inside the loop and swallow exceptions in all but the last iteration. Don't retry forever.

3. background threads typically need to report back to their parent thread, whether success or failure. You shouldn't have a background thread retry forever, or just fail or give up without telling.

This makes sense
so could I use recursion to do a retry. I dont want it to retry it forever... just wait a sec and then try to connect again. If it fails again then exit.

Luc Pattyn12-Mar-09 5:23

Luc Pattyn

12-Mar-09 5:23

Hi,

I see no problem in retrying a couple of times, and only report failure if all tries have failed.
I would not actually use recursion for that though, recursion gets abused all too often.
Basically what I'd do is (in C# syntax, VB.NET can do similar things):

for (int tryCount=1; ; tryCount++) {
    try {
        ...
    } catch(Exception exc) (
        if (tryCount< maxTry) continue;
        log(exc.ToString());
        throw new ApplicationException("Operation XXX failed after "+maxTry+" tries", exc);
    }
}
// getting here on success only

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captainmogo12-Mar-09 8:14

How to export to word using VB 2008

12-Mar-09 8:14

Thanks for your help. I used your example and it works well. If it cannot see/find the database after 2 tries, it throws an exception which is caught by the run worker completed event and the rest of the DoWork method is not executed (which is fine since the whole point is to access the database anyway)

Thanks again

Manfred ramirez11-Mar-09 8:45

Manfred ramirez

11-Mar-09 8:45

Hello I am trying to create a windows form application with VB 2008 and i am intending to read info from any textbox or whatever and export the data to word I do not know how to do it, I did some research and this is what I found :
Dim oWord As Word._Application()
oWord = New Word.Application()

But is giving me errors the word.application declaration seems to work with older version but not 2008. Please help.

I also found this code but it does not work:

Public Module DriveWord

Public Sub Main()

'Start Word in the background
Dim App As New Word.Application()
App.DisplayAlerts = Word.WdAlertLevel.wdAlertsNone

'Create a new document
Dim Doc As Word._Doucment = App.Documents.Add()

Console.WriteLine()
Console.Writeline("Creating New Document")
Console.Writeline()

'Add a heading and two lines of text
Dim Range As Word.Range = Doc.Paragraphs.Add().Range

Range.InsertBefore ("Test Document")
Range.Style = "Heading 1"

Range = Doc.Paragraphs.Add().Range
Range.InsertBefore("Line one." &vbCrLf & "Line two.")
Range.Font.Bold = True

'Save and close the current document.
Doc.SaveAs(App.StartupPath & "\test.doc")
Doc.Close()
Doc=Nothing

End Sub

regards,

Re: How to export to word using VB 2008

Luc Pattyn11-Mar-09 9:41

Luc Pattyn

11-Mar-09 9:41

Hi,

FWIW: I recently decided to create RTF files from C#, foregoing all .NET-to-various-Office-versions troubles. Once an RTF file exists, you can launch it using Process.Start(filename) which launches the default RTF application, i.e. WordPad if no Office is present, Office otherwise. And BTW: RTF is capable of much more than you can edit in WordPad, e.g. I did some table stuff which is visible in WordPad, and works fine (viewing and editing) in Word, any version.

Smile | :)

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transfer data from xml to database table

madhuchandran11-Mar-09 6:49

madhuchandran

11-Mar-09 6:49

hai,
i have a xml doc i need the nodes in the xml to be converted to a database table records for example access or oracle or sql. any one know the vb.net code to do this??

Re: transfer data from xml to database table

Jon_Boy11-Mar-09 7:01

Jon_Boy

11-Mar-09 7:01

Tons of ways and you'll need to read up on it, because there are entirely to many details to list here and each DB has diff. methods for doing this.

1. You could do an XML reader and handle the import yourself.
2. SQL - you can use SSIS to import the data.
3. You could do an XML transform for the import.

Any suggestions, ideas, or 'constructive criticism' are always welcome.

"There's no such thing as a stupid question, only stupid people." - Mr. Garrison

How to ping every computer in a LAN

Amer Rehman11-Mar-09 6:41

Amer Rehman

11-Mar-09 6:41

Hi
I am using visual studio 2003. I need to ping every computers in my LAN for my application. For this purpose I have used the "System.Net" namespace's TCP class. Is there any better solution to this problem.

Thanks.

reman

Re: How to ping every computer in a LAN

0x3c011-Mar-09 6:59

0x3c0

11-Mar-09 6:59

I'm not certain of the method you're talking about, but chances are the System.Net.NetworkInformation.Ping class will be more verbose and robust

Re: How to ping every computer in a LAN

Expert Coming11-Mar-09 22:35

Expert Coming

11-Mar-09 22:35

If they all ran an app you write, you could use UDP.

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.NET Remoting help

OorSkietKoS11-Mar-09 5:42

OorSkietKoS

11-Mar-09 5:42

Hi everyone, i need to create a project on .NET remoting. I am a newbie at VB.NET and need some help. Here is the specifications:

Must be in the console Console

Write a console client that lets the user input a String value for the path of a text file.
This path must be passed to a Function which displays the contents of the specified file.

If possible please provide coding examples.

thanks in advance.

Johan Hakkesteegt11-Mar-09 7:41

Johan Hakkesteegt

11-Mar-09 7:41

Sorry we do not do your homework for you.

My advice is free, and you may get what you paid for.

OorSkietKoS11-Mar-09 20:25

OorSkietKoS

11-Mar-09 20:25

Well, Im just looking for some guidelines, as my VB.NET book does not cover .NET Remoting. The example they give is so simple and i have tried searching the net, with no luck.

Johan Hakkesteegt12-Mar-09 2:18

Johan Hakkesteegt

12-Mar-09 2:18

In that case, don't get stuck at the title of the assignment. Look at the specifications.
In other words, (apparently) you need to make a console program that takes a string parameter (path to a text file) and returns the contents of that file to the screen.

So:
1. look into console programming. For example just start a new console project in Visual Studio.
2. Figure out how you can pass parameters to a console program. For example look into command line arguments.
3. figure out how to find a file and read from it. For example look into System.IO and the StreamReader class
4. Use Console.Write or Console.WriteLine to return the content of the file to the screen.

My advice is free, and you may get what you paid for.

Dave Kreskowiak12-Mar-09 3:40

Dave Kreskowiak

12-Mar-09 3:40

Your spec's don't have anything to do with Remoting. All you're doing it taking a filepath as a command line argument, opening that file and reading it into a String, then using Console.WriteLine to write that string out. .NET Remoting is WAY overkill for such a simple assignment.

BTW, there's nothing in this code that would not have been covered in the chapters of the book you're using up to this point. So, if you're in Chapter 5, the answer is not going to be in Chapters 6 and above.

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Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008

OorSkietKoS12-Mar-09 4:40

OorSkietKoS

12-Mar-09 4:40

Thanks alot, I know Remoting makes it way overkill, but they asked us to do it in remoting, I can easily get this doen trough console alone. The thing is My VB.NET book does not really cover Remoting in advance. the example they give is simple and does not really explain anything in detail. But thanks alot anyway guys. Appreciated alot. Smile | :)