Database exception handling

[A.]

Hi all,

I'm using tg1.1 with sqlalchemy
I'm trying to manage all exceptions using @exception_handler
decorator. It works fine for ValueError, TypeError etc.
But for now I am unable to deal with Database Errors using this same
technique:

here's how the code looks like:

1) Definition of the handler, in model.py, before the Root
controller:

def general_except_handler(self,tg_exceptions=None,**kw):
log.error(u'*'+str(datetime.datetime.now())+u'* '+str
(request.path) + u" Exception: " + unicode(str
(tg_exceptions),'latin'))
flash(u"exception::Exception: " + unicode(str
(tg_exceptions),'latin'))
redirect('/')
return dict()

2) Definition, just below the handler, of the catching expression

catch_excep_expr="isinstance(tg_exceptions, (KeyError,TypeError))"

3) I then use it for the controllers with exception_handler decorator

@expose(template="resyweb.templates.generic_form_display")
@exception_handler(general_except_handler,catch_excep_expr)
@identity.require(identity.in_group("admin"))
def edit_reviewer(self,**kw):

It works fine but when I try to include something like SQLAlchemyError
(previously imported with

from sqlalchemy.exceptions import SQLAlchemyError ), I cannot start
the application:

...
in Root
@identity.require(identity.in_group("admin"))
File "c:\python25\lib\site-packages\TurboGears-1.1-py2.5.egg
\turbogears\errorh
andling.py", line 133, in register
dispatch_error_adaptor(handler or func))
File "C:\Python25\lib\site-packages\decoratortools-1.7-py2.5.egg\peak
\util\dec
orators.py", line 601, in do_decorate
File "build\bdist.win32\egg\peak\rules\core.py", line 197, in
callback
File "build\bdist.win32\egg\peak\rules\core.py", line 190, in
register_for_cla
ss
File "build\bdist.win32\egg\peak\rules\core.py", line 65, in
parse_rule
File "build\bdist.win32\egg\peak\rules\core.py", line 153, in
__call__
File "build\bdist.win32\egg\peak\rules\predicates.py", line 517, in
_parse_str
ing
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 424, in
parse_exp
r
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 419, in
build
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 51, in
com_binary

File "build\bdist.win32\egg\peak\rules\predicates.py", line 189, in
And
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 419, in
build
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 217, in
atom
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 419, in
build
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 51, in
com_binary

File "build\bdist.win32\egg\peak\rules\predicates.py", line 189, in
And
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 419, in
build
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 217, in
atom
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 419, in
build
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 178, in
power
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 284, in
com_call_
function
File "build\bdist.win32\egg\peak\rules\predicates.py", line 199, in
CallFunc
File "build\bdist.win32\egg\peak\rules\predicates.py", line 233, in
apply_meta

File "build\bdist.win32\egg\peak\rules\predicates.py", line 213, in
parse
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 419, in
build
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 217, in
atom
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 419, in
build
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 356, in
testlist_
gexp
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 51, in
com_binary

File "build\bdist.win32\egg\peak\rules\codegen.py", line 428, in
method
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 419, in
build
File "build\bdist.win32\egg\peak\rules\ast_builder.py", line 10, in
<lambda>
File "build\bdist.win32\egg\peak\rules\codegen.py", line 347, in
Name
NameError: SQLAlchemyError

Would anyone know how to find a solution for this problem, or maybe
another technique for catching application-wide database exceptions?

Thanks

Adrien

[Diez B. Roggisch]

I *think* this is because you need to have the name SQLAlchemy defined in the
module you define the handler in. So do you import it in your controller
file?

Diez

[A.]

Hi Diez,

Yes (if I understand correcly your point) I import the error class
just before defining the exception-catching expression, at the top of
controllers.py (Outside of the Root controller, and declaring it
inside the Root controller doesn't change anything either):

from sqlalchemy.orm.exc import NoResultFound
catch_excep_expr="isinstance(tg_exceptions,
(KeyError,TypeError,NoResultFound))"

By the way I'm not getting an import error, but a NameError

[Diez B. Roggisch]

> Would anyone know how to find a solution for this problem, or maybe
> another technique for catching application-wide database exceptions?

I'm sorry, I didn't catch the sentence that you already imported the exception
in the first post.

I don't know what to do else, except from making some nasty hack like

"SQLAlchemyError" in tg_exceptions.__class__.__name__

which is of course ugly because it doesn't work for sub-classes.

Other than that, I'd try to find more information about peak rules.

Diez

[A.]

Thanks Diez I'll have a look that way. What's strange is that in the
past I've been able to handle database error with this technique,
while using Sqlobject as orm :

IntegrityError =model.hub.getConnection
()._dbConnection.module.IntegrityError
ProgrammingError =model.hub.getConnection
()._dbConnection.module.ProgrammingError
from sqlobject import SQLObjectNotFound
from sqlobject.dberrors import DuplicateEntryError

catch_excep_expr="isinstance(tg_exceptions,
(KeyError,SQLObjectNotFound,DuplicateEntryError,IntegrityError,ValueError,ProgrammingError))"

And it worked with no trouble, I wonder what makes it different with
sqlalchemy...

If anyone has another idea about this, or technique to handle
application-wide db errors, I'll be glad to read about it!

Adrien

[A.]

The answer to this question can be found here:

http://groups.google.com/group/turbogears/browse_thread/thread/9a2dc934bcd535bb

[timo...@googlemail.com]

hi,
here a global exception handler that i used in tg 1.0.9

@tg.errorhandling.dispatch_error.when("tg_exceptions is not None")
def exception(self , tg_source, tg_errors, tg_exception, *args,
**kw):
# do some stuff.

return dict(tg_template="myproject.templates.error.500")

this will catch all exceptions inside that controller, you could
distinct between different exception types inside exception() method.

timor