cppcms-users

[Cppcms-users] How to catch CPPDB errors

[Marcel H. <ke...@co...>]

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Hi everyone,

I'd like to know the "correct" way of handling errors in cppdb
statements.
If I do something like this:
  "INSERT INTO ...." << cppdb::exec;
and there will be an error, a 500 respond will be given to the client.
Not that nice.
Next try was to catch the exception:

  try {
    "INSERT INTO ...." << cppdb::exec;
  } catch(cppdb::cppdb_error const &e) {
    //what can we do here?
  }

Nice try, but cppdb_error has only the method what() and what gives me
back a char* with the error description. But there could be more than
one error in that query. That's why there are error codes. But
unfortunately every sql provider has different error codes.
Another problem with cppdb error is that the message will be
localized, so you cannot parse it.

So... what is the right way to do this?

Regards
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Re: [Cppcms-users] How to catch CPPDB errors

[Artyom B. <art...@ya...>]

I would suggest in general...

Not get into situations where you can get a error, or at least if you expect a error catch it.

What kind of errors can happen:

	1. Constrain violation:

	* Check it before from a transaction assuming isolation
	* Catch at specific point - assume that the error is constraint violation.
	2. Deadlock - due to colliding statements - not much to do. Or let 500 response to happen or catch a cppdb error at the root of you app hierarchy main and say (oops)
	3. Connection errors or other stuff - 500 is more than reasonable - or do it what you did in 2

Now about specific errors.

Probably it would be good idea to derive several sub exceptions like:

cppdb::constraint_error
cppdb::deadlock_error  
cppdb::connection_error

Similarly to the current set: http://cppcms.com/sql/cppdb/classcppdb_1_1cppdb__error.html

Maybe some more I can't think about them right now.

But this requires some code writing and what is even more important - updating each backend and probably
the most hard would be ODBC.

Any volunteers?

 
Artyom Beilis
--------------
CppCMS - C++ Web Framework:   http://cppcms.com/
CppDB - C++ SQL Connectivity: http://cppcms.com/sql/cppdb/



>________________________________
> From: Marcel Hellwig <ke...@co...>
>To: cpp...@li... 
>Sent: Wednesday, January 23, 2013 2:35 PM
>Subject: [Cppcms-users] How to catch CPPDB errors
> 
>-----BEGIN PGP SIGNED MESSAGE-----
>Hash: SHA1
>
>Hi everyone,
>
>I'd like to know the "correct" way of handling errors in cppdb
>statements.
>If I do something like this:
>  "INSERT INTO ...." << cppdb::exec;
>and there will be an error, a 500 respond will be given to the client.
>Not that nice.
>Next try was to catch the exception:
>
>  try {
>    "INSERT INTO ...." << cppdb::exec;
>  } catch(cppdb::cppdb_error const &e) {
>    //what can we do here?
>  }
>
>Nice try, but cppdb_error has only the method what() and what gives me
>back a char* with the error description. But there could be more than
>one error in that query. That's why there are error codes. But
>unfortunately every sql provider has different error codes.
>Another problem with cppdb error is that the message will be
>localized, so you cannot parse it.
>
>So... what is the right way to do this?
>
>Regards
>-----BEGIN PGP SIGNATURE-----
>Version: GnuPG v1.4.13 (GNU/Linux)
>Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/
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Re: [Cppcms-users] How to catch CPPDB errors

[Marcel H. <ke...@co...>]

Am 23.01.2013 14:50, schrieb Artyom Beilis:
> I would suggest in general...
> 
> Not get into situations where you can get a error, or at least if you
> expect a error catch it.
Think of registration. A Username should be unique and a email adrress
should be unique too. I will not check this, because IMO this is a task
for the database.
> 
> What kind of errors can happen:
> 
>  1. Constrain violation:
>       * Check it before from a transaction assuming isolation
>       * Catch at specific point - assume that the error is constraint
>         violation.
>  2. Deadlock - due to colliding statements - not much to do. Or let 500
>     response to happen or catch a cppdb error at the root of you
>     app hierarchy main and say (oops)
>  3. Connection errors or other stuff - 500 is more than reasonable - or
>     do it what you did in 2
> 
> Now about specific errors.
> 
> Probably it would be good idea to derive several sub exceptions like:
> 
> cppdb::constraint_error
> cppdb::deadlock_error  
> cppdb::connection_error
Could be good, but there are over 100 errors that can happen while you
execute a statement. But i will have a look and see what i can do.
> 
> Similarly to the current
> set: http://cppcms.com/sql/cppdb/classcppdb_1_1cppdb__error.html
> 
> Maybe some more I can't think about them right now.
> 
> But this requires some code writing and what is even more important -
> updating each backend and probably
> the most hard would be ODBC.
> 
> Any volunteers?
> 
>  
> Artyom Beilis

Marcel