DuplicateKeyError exception

[lestat]

Hi!

I use postgresql and I try create my exception DuplicateKeyError inheritanced from IntegrityError.

I know that duplicate key in postgresql has code 23505 and I must catch with

if err.orig.pgcode == '23505':

    ...

How I can create this?

I don't work with many exceptions, and don't find what method it execute when it raised.

I try:

from sqlalchemy.exc import IntegrityError

class DuplicateKeyError(IntegrityError):

    def __init__(self, *args, **kwargs):

        print '______________DuplicateKeyError init called'

        print '____ args:',args

        print '____ kwargs:',kwargs

        super(DuplicateKeyError, self).__init__(*args, **kwargs)

    @classmethod

    def instance(cls, *args, **kwargs):

        print '______________DuplicateKeyError instance called'

        print '____ cls:',cls

        print '____ args:',args

        print '____ kwargs:',kwargs

        super(DuplicateKeyError, cls).instance(*args, **kwargs)

    @staticmethod

    def __new__(cls, *args, **kwargs):

        print '______________DuplicateKeyError new called'

        print '____ cls:',cls

        print '____ args:',args

        print '____ kwargs:',kwargs

        super(DuplicateKeyError, cls).__new__(*args, **kwargs)

    def __call__(self, *args, **kwargs):

        print '______________DuplicateKeyError call called'

        print '____ self:',self

        print '____ args:',args

        print '____ kwargs:',kwargs

        super(DuplicateKeyError, self).__call__(*args, **kwargs)

def test():

    try:

        i = Interest(name='x1')

        db.session.add(i)

        db.session.commit()

    except DuplicateKeyError as err:

        print '===== err:',err

        print '===== err.orig.pgcode:',err.orig.pgcode

but nothing of my prints does not executed.

Where I wrong?

Thanks!

[Michael Bayer]

if you want to rethrow DBAPI exceptions you'd need to catch it at some point.   We don't have a hook where you can build in a "try:/except:" around executions right now so such a thing would need to be called externally to SQLAlchemy:

def execute(connection, stmt):

   try:

        return connection.execute(stmt)

   except IntegrityError, err:

        if err.orig.pgcode == '23505':

            raise DuplicateKeyError()

       else:

            raise

which doesn't really get at session.commit().   There's ways to monkeypatch such a function into the Connection itself, though that's kind of brittle.

Since catching this error is something you want to do occasionally I'd likely just build a context manager:

class catch_dupes(object):

    def __enter__(self):

        return None

    def __exit__(self, type, value, traceback):

        if issubclass(type, IntegrityError) and \

            value.orig.pgcode == "23505":

            raise DuplicateKeyError()

try:

with catch_dupes():

db.session.commit()

except DuplicateKeyError:

# ...

pretty ugly. if anyone else has some nifty python tricks here feel free.

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[lestat]

if you want to rethrow DBAPI exceptions you'd need to catch it at some point.   We don't have a hook where you can build in a "try:/except:" around executions right now so such a thing would need to be called externally to SQLAlchemy:

Ok, thanks!