Thanks Michael for your time. Yes, I am using scope session to create Session. I want that all types of write operations *(insert, delete, update)* should run on write engine and only read operations will perform on read engine.
class SQLAlchemySessionRouter(Session): def get_bind(self, mapper=None, clause=None): if self._flushing: return ENGINES['write-only'] else: return ENGINES['read-only'] So the problem with above mentioned class is that when I run any update or delete query like query.update() and query.delete() then it uses read engine instead of write engine. So to fulfill my requirement I have modified above class like this. class SQLAlchemySessionRouter(Session): def get_bind(self, mapper=None, clause=None): if self._flushing: return ENGINES['write-only'] elif isinstance(clause, sqlalchemy.sql.expression.Update): return ENGINES['write-only'] elif isinstance(clause, sqlalchemy.sql.expression.Delete): return ENGINES['write-only'] else: return ENGINES['read-only'] I need your opinion Michael, Are these modification good? Should I go with them? *Or is there any better way to do this?* Looking forward to your thoughts. On Sunday, February 15, 2015 at 1:11:53 AM UTC+5, Michael Bayer wrote: > > > > ahmadj...@gmail.com <javascript:> wrote: > > > Hi, > > > > I am working on a web site using Python Django and SQLAlchemy ORM. I > want to do all read operations in separate database and write operations in > separate database. > > So I tried Mike Bayer's solution ( > http://techspot.zzzeek.org/2012/01/11/django-style-database-routers-in-sqlalchemy/) > > but query.update() and query.delete() didn't work properly. I debugged some > code and modified SessionRouter class as following: > > > > class SQLAlchemySessionRouter(Session): > > > > def get_bind(self, mapper=None, clause=None): > > if self._flushing: > > return ENGINES['write-only'] > > elif isinstance(clause, sqlalchemy.sql.expression.Update): > > return ENGINES['write-only'] > > elif isinstance(clause, sqlalchemy.sql.expression.Delete): > > return ENGINES['write-only'] > > else: > > return ENGINES['read-only'] > > > > Now it is working fine in my case (I tested this manually). > > > > I need Mike Bayer or experts guidance. Do these modifications looks > good? Should I go with this solution? Or is there some thing better that > can help me? > > > Where this can go wrong is if you are using the Session in a transaction, > it will run all your SELECT queries on the read engine, and the flushes on > the write engine, but depending on how your replication and transaction > isolation is set up, you might not see the rows that you just committed. > > I think the blog post mentions this, I should probably update it to > accommodate using transactions appropriately. if the recipe works for > you as is, then keep it in place. > > > > > > > Thanks in advance, > > > > > > -- > > You received this message because you are subscribed to the Google > Groups "sqlalchemy" group. > > To unsubscribe from this group and stop receiving emails from it, send > an email to sqlalchemy+...@googlegroups.com <javascript:>. > > To post to this group, send email to sqlal...@googlegroups.com > <javascript:>. > > Visit this group at http://groups.google.com/group/sqlalchemy. > > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
