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POshould SQLAlchemy session.begin_nested() be committed with transaction.commit() when using pyramid_tm?
 

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  1. POshould SQLAlchemy session.begin_nested() be committed with transaction.commit() when using pyramid_tm?
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    <p>I'm developing a pyramid application and currently in the process of moving from sqlite to postgresql. I've found postgresql more restrictive transaction management is giving me a bad time.</p> <p>I am using the pyramid_tm because I find it convenient. Most of my problems occur during my async calls. What I have is views that serve up dynamic forms. The idea is - if we got an id that corresponds to a database row we edit the existing row. Otherwise, we are adding a new guy.</p> <pre><code>@view_config(route_name='contact_person_form', renderer='../templates/ajax/contact_person_form.pt', permission='view', request_method='POST') def contact_person_form(request): try: contact_person_id = request.params['contact_person'] DBSession.begin_nested() contact_person = DBSession.query(ContactPerson).filter(ContactPerson.id == contact_person_id).one() transaction.commit() except (NoResultFound, DataError): DBSession.rollback() contact_person = ContactPerson(name='', email='', phone='') return dict(contact_person=contact_person) </code></pre> <p>I need to begin a nested transaction because otherwise my lazy request method which is registered with <code>config.add_request_method(get_user, 'user', reify=True)</code> and called when rendering my view</p> <pre><code>def get_user(request): userid = unauthenticated_userid(request) if userid is not None: user = DBSession.query(Employee).filter(Employee.id == userid).first() return user </code></pre> <p>complains that the transaction has been interrupted and the SELECT on employees will be skipped.</p> <p>I have two questions:</p> <ol> <li>Is it okay to do <code>transaction.commit()</code> on a <code>session.begin_nested()</code> nested transaction? I don't exactly where SQLAlchemy ends and pyramid_tm begins. If I try to commit the session I get an exception that says I can only commit using the transaction manager. On the other hand DBSession.rollback() works fine.</li> <li><p>Does handling this like</p> <pre><code>try: #do something with db except: #oops, let's do something else </code></pre></li> </ol> <p>make sense? I have the feeling this is 'pythonic', but I'm not sure if this underlying transaction thing calls for non-pythonic means.</p>
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