Re: [sqlalchemy] recommended declarative method design pattern for sessions
On Mar 23, 2010, at 9:29 AM, King Simon-NFHD78 wrote: object_session does indeed return the session that the instance is already bound to (so you shouldn't close it). I didn't know what object_session would return if the original session had been closed, so I tried it: Thanks for looking into this for me. As an update, I have been trying to use object_session but have been struggling with bugs related to the session returned from object_session() turning to None, presumably because it is somehow getting garbage collected. Because of this, I am going to try to use scoped_session() as this seems to be the preferred method for keeping things simple and reliable with session sharing between disparate pieces of code. This way, all my code can create a new session but will end up getting the same session, thus solving the complexity of grabbing the current object's session (I hope.) -Daniel -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
RE: [sqlalchemy] recommended declarative method design pattern for sessions
Daniel Robbins wrote: Hi All, One of the things that doesn't seem to be covered in the docs, and that I'm currently trying to figure out, is the recommended design pattern to use for managing sessions from declarative methods calls. Consider a declarative class User, where I want to implement a FindFriends() method: class User(Base): # declarative fields defined here def FindFriends(self): session = Session() # it's handy to use the self reference in query methods: friends = session.query(Friends).filter_by(friend=self).all() session.close() return friends Certainly, these types of methods would seem to be useful, but here's a dilemma - the above code doesn't work. Because the method uses a new session, which is guaranteed to not be the same session that was used to retrieve the original User object, the following code will fail: session = session() me = session.query(User).filter_by(name=Daniel).first() me.FindFriends() See the 'How can I get the Session for a certain object' question at http://www.sqlalchemy.org/docs/session.html#frequently-asked-questions Basically, in your FindFriends method, replace: session = Session() with: session = Session.object_session(self) Hope that helps, Simon -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
Re: [sqlalchemy] recommended declarative method design pattern for sessions
On Mar 22, 2010, at 5:10 AM, King Simon-NFHD78 wrote: See the 'How can I get the Session for a certain object' question at http://www.sqlalchemy.org/docs/session.html#frequently-asked-questions Basically, in your FindFriends method, replace: session = Session() with: session = Session.object_session(self) The reference documentation seems to indicate that Session.object_session() will return the existing session if one exists, rather than providing a new session that must be separately closed. Is this correct? If so, then FindFriends() should not close the session acquired via Session.object_session(obj), correct? Is it possible for object_session() to return None if the object's session was previously close()d? Thanks, Daniel -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] recommended declarative method design pattern for sessions
Hi All, One of the things that doesn't seem to be covered in the docs, and that I'm currently trying to figure out, is the recommended design pattern to use for managing sessions from declarative methods calls. Consider a declarative class User, where I want to implement a FindFriends() method: class User(Base): # declarative fields defined here def FindFriends(self): session = Session() # it's handy to use the self reference in query methods: friends = session.query(Friends).filter_by(friend=self).all() session.close() return friends Certainly, these types of methods would seem to be useful, but here's a dilemma - the above code doesn't work. Because the method uses a new session, which is guaranteed to not be the same session that was used to retrieve the original User object, the following code will fail: session = session() me = session.query(User).filter_by(name=Daniel).first() me.FindFriends() It would seem to be handy if SQLAlchemy placed a reference in each declarative object of the session from which it originated when query was called, so then my code could do something like this: class User(Base): # declarative fields defined here def FindFriends(self): # note the self.session.query - the idea is that sqlalchemy's query() would initialize this for us return self.session.query(Friends).filter_by(friend=self).all() Then this would allow the following code to work: session = session() me = session.query(User).filter_by(name=Daniel).first() me.FindFriends() This would work because me.FindFriends() would now have easy access to the same session that was used to retrieve me -- so the objects would be compatible and could be easily combined in queries. This would allow many methods to be added to the User class that could all do various kinds of db queries without having to pass a session variable around manually. My question is - what is the recommended design pattern to do what I am trying to do above? Passing the current session as an argument to FindFriends() seems cumbersome - is that the recommended approach or is there a more elegant way to handle it? Is my handy suggestion above something that would actually be useful or is there a better way to do what I am wanting to do? (I'm trying to be a good SQLAlchemy coder and not use a global session=Session() for everything, as explained here: http://www.sqlalchemy.org/docs/session.html#frequently-asked-questions . But to do this, I need to find a good design pattern to use in place of a global :) Thanks and Regards, Daniel -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
