On Sat, Jul 27, 2019, at 4:53 PM, Nestor Diaz wrote:
> Hello everybody.
>
> I am experimenting with sqlalchemy and pyramid, following the tutorial
> steps at:
>
> https://docs.pylonsproject.org/projects/pyramid/en/latest/quick_tutorial/databases.html
>
> The example above is a wiki, with a set of pages, every page have a
> 'title' and a 'body' and the 'title' have a 'unique' constraint at
> database level.
>
> Let's suppose that I added two pages, i.e. pages =
> [{id:1,title:'titleA',body:'bodyA'}, {id:2,title:'titleB',body:'bodyB'}
> , then I decide to update id number 2 and set title to 'titleA' which is
> the same as id number 1, it then raise an exception, however I can not
> catch the exception, even if I set up a try-catch block, however if I
> add a DBSession.flush() inside the try, the sql sentence is executed and
> therefore I can catch the exception.
>
> I am copying the code with the 'Uncaught Exception' and the code with
> the 'Caught Exception'.
>
> The question is: Do I have to 'flush()' everytime to be sure the sql
> sentence is executed, or there is a better way, or which way do you
> suggest to manage the exceptions ?
Usually you wouldn't have a catch that is specific to an error like that, your
pyramid application would have a generic error page routine that occurs for all
requests, and it would occur normally at the point at which the Session is
committed. It looks like you essentially want a custom error page scheme here
which I would think would be something that happens more at the pyramid level,
e.g. in your controller you add some kind of token "use_this_error_page" so
that Pyramid's usual error page routine can direct to this special page.
When people do catch IntegrityError specifically, it is often because they want
to try to insert a row and then switch to an UPDATE if the row already exists,
and in this pattern you normally want to use a savepoint, but that doesn't seem
like what's happening here.
Ultimately, for the code given, the answer is yes, you would need to flush to
emit the SQL at this specific place if that's what you need, but I would seek
out cleaner patterns from the Pyramid community.
>
> Thanks for your time and attention.
>
> This is the python code:
>
> [...]
>
> # Change the content and redirect to the view
>
> try:
> from sqlalchemy.exc import IntegrityError
> page.title = appstruct['title']
> page.body = appstruct['body']
> DBSession.flush()
> url = self.request.route_url('wikipage_view', uid=uid)
> return HTTPFound(url)
> except IntegrityError as exc:
> import traceback
> traceback.print_exc()
> error = colander.Invalid(wiki_form.schema)
> error['title'] = exc.args[0]
> wiki_form.error = error
> wiki_form.widget.handle_error(wiki_form, error)
> rendered_form = wiki_form.render()
> return dict(page=page,
> form=rendered_form)
>
>
> [...]
>
> The tracebacks:
>
> 1. Uncaught Exception:
>
> 2019-07-27 01:29:41,231 INFO [sqlalchemy.engine.base.Engine][waitress]
> UPDATE wikipages SET title=? WHERE wikipages.uid = ?
> 2019-07-27 01:29:41,231 INFO [sqlalchemy.engine.base.Engine][waitress]
> ('titleA', 2)
> 2019-07-27 01:29:41,232 INFO [sqlalchemy.engine.base.Engine][waitress]
> ROLLBACK
> 2019-07-27 01:29:41,306 ERROR [pyramid_debugtoolbar][waitress] Uncaught
> sqlalchemy.exc.IntegrityError at http://127.0.0.1:6543/2/edit
> traceback url:
> http://127.0.0.1:6543/_debug_toolbar/313430303936383730393639343136/exception
> Traceback (most recent call last):
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
> line 1244, in _execute_context
> cursor, statement, parameters, context
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/default.py",
> line 550, in do_execute
> cursor.execute(statement, parameters)
> sqlite3.IntegrityError: UNIQUE constraint failed: wikipages.title
>
> The above exception was the direct cause of the following exception:
>
> Traceback (most recent call last):
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/pyramid_debugtoolbar/toolbar.py",
> line 257, in toolbar_tween
> response = _handler(request)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/pyramid_debugtoolbar/panels/performance.py",
> line 58, in resource_timer_handler
> result = handler(request)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/pyramid_tm/__init__.py",
> line 171, in tm_tween
> reraise(*exc_info)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/pyramid_tm/compat.py",
> line 36, in reraise
> raise value
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/pyramid_tm/__init__.py",
> line 152, in tm_tween
> return _finish(request, manager.commit, response)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/pyramid_tm/__init__.py",
> line 96, in _finish
> reraise(*exc_info)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/pyramid_tm/compat.py",
> line 36, in reraise
> raise value
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/pyramid_tm/__init__.py",
> line 76, in _finish
> finisher()
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/transaction/_manager.py",
> line 252, in commit
> return self.manager.commit()
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/transaction/_manager.py",
> line 131, in commit
> return self.get().commit()
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/transaction/_transaction.py",
> line 311, in commit
> reraise(t, v, tb)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/transaction/_compat.py",
> line 50, in reraise
> raise value
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/transaction/_transaction.py",
> line 302, in commit
> self._commitResources()
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/transaction/_transaction.py",
> line 447, in _commitResources
> reraise(t, v, tb)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/transaction/_compat.py",
> line 50, in reraise
> raise value
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/transaction/_transaction.py",
> line 419, in _commitResources
> rm.tpc_begin(self)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/zope/sqlalchemy/datamanager.py",
> line 106, in tpc_begin
> self.session.flush()
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/session.py",
> line 2459, in flush
> self._flush(objects)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/session.py",
> line 2597, in _flush
> transaction.rollback(_capture_exception=True)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/util/langhelpers.py",
> line 68, in __exit__
> compat.reraise(exc_type, exc_value, exc_tb)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/util/compat.py",
> line 154, in reraise
> raise value
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/session.py",
> line 2557, in _flush
> flush_context.execute()
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/unitofwork.py",
> line 422, in execute
> rec.execute(self)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/unitofwork.py",
> line 589, in execute
> uow,
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/persistence.py",
> line 236, in save_obj
> update,
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/persistence.py",
> line 996, in _emit_update_statements
> statement, multiparams
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
> line 988, in execute
> return meth(self, multiparams, params)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/sql/elements.py",
> line 287, in _execute_on_connection
> return connection._execute_clauseelement(self, multiparams, params)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
> line 1107, in _execute_clauseelement
> distilled_params,
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
> line 1248, in _execute_context
> e, statement, parameters, cursor, context
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
> line 1466, in _handle_dbapi_exception
> util.raise_from_cause(sqlalchemy_exception, exc_info)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/util/compat.py",
> line 399, in raise_from_cause
> reraise(type(exception), exception, tb=exc_tb, cause=cause)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/util/compat.py",
> line 153, in reraise
> raise value.with_traceback(tb)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
> line 1244, in _execute_context
> cursor, statement, parameters, context
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/default.py",
> line 550, in do_execute
> cursor.execute(statement, parameters)
> sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) UNIQUE
> constraint failed: wikipages.title
> [SQL: UPDATE wikipages SET title=? WHERE wikipages.uid = ?]
> [parameters: ('titleA', 2)]
> (Background on this error at: http://sqlalche.me/e/gkpj)
>
> 2. Caught Exception
>
> 2019-07-27 02:18:33,208 INFO [sqlalchemy.engine.base.Engine][waitress]
> UPDATE wikipages SET title=? WHERE wikipages.uid = ?
> 2019-07-27 02:18:33,209 INFO [sqlalchemy.engine.base.Engine][waitress]
> ('titleA', 2)
> 2019-07-27 02:18:33,209 INFO [sqlalchemy.engine.base.Engine][waitress]
> ROLLBACK
> Traceback (most recent call last):
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
> line 1244, in _execute_context
> cursor, statement, parameters, context
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/default.py",
> line 550, in do_execute
> cursor.execute(statement, parameters)
> sqlite3.IntegrityError: UNIQUE constraint failed: wikipages.title
>
> The above exception was the direct cause of the following exception:
>
> Traceback (most recent call last):
> File
> "/home/ndiaz/tutrest/quick_tutorial/authentication/tutorial/views.py",
> line 228, in wikipage_edit
> DBSession.flush()
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/scoping.py",
> line 162, in do
> return getattr(self.registry(), name)(*args, **kwargs)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/session.py",
> line 2459, in flush
> self._flush(objects)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/session.py",
> line 2597, in _flush
> transaction.rollback(_capture_exception=True)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/util/langhelpers.py",
> line 68, in __exit__
> compat.reraise(exc_type, exc_value, exc_tb)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/util/compat.py",
> line 154, in reraise
> raise value
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/session.py",
> line 2557, in _flush
> flush_context.execute()
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/unitofwork.py",
> line 422, in execute
> rec.execute(self)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/unitofwork.py",
> line 589, in execute
> uow,
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/persistence.py",
> line 236, in save_obj
> update,
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/orm/persistence.py",
> line 996, in _emit_update_statements
> statement, multiparams
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
> line 988, in execute
> return meth(self, multiparams, params)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/sql/elements.py",
> line 287, in _execute_on_connection
> return connection._execute_clauseelement(self, multiparams, params)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
> line 1107, in _execute_clauseelement
> distilled_params,
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
> line 1248, in _execute_context
> e, statement, parameters, cursor, context
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
> line 1466, in _handle_dbapi_exception
> util.raise_from_cause(sqlalchemy_exception, exc_info)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/util/compat.py",
> line 399, in raise_from_cause
> reraise(type(exception), exception, tb=exc_tb, cause=cause)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/util/compat.py",
> line 153, in reraise
> raise value.with_traceback(tb)
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
> line 1244, in _execute_context
> cursor, statement, parameters, context
> File
> "/home/ndiaz/tutrest/env35/lib/python3.5/site-packages/sqlalchemy/engine/default.py",
> line 550, in do_execute
> cursor.execute(statement, parameters)
> sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) UNIQUE
> constraint failed: wikipages.title
> [SQL: UPDATE wikipages SET title=? WHERE wikipages.uid = ?]
> [parameters: ('titleA', 2)]
> (Background on this error at: http://sqlalche.me/e/gkpj)
>
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
> description.
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>
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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