Thank you, everyone, for your extremely helpful responses. You really helped clear this matter up
On Thursday, March 27, 2014 9:27:42 AM UTC-4, Darin Gordon wrote: > > Let me preface this by saying that I researched to the best of my > abilities the answers to my following inquiries. I would not ask for help > without first trying to investigate this on my own. Asking through this > forum is the proverbial end of the line, so thanks for taking any time to > read and respond. > > I understand relational databases and have been bridging a knowledge gap > with ORMs, using SQLAlchemy. I've struggled a bit while learning what > exactly is going on in the ORM when ADDING new associations in a M to N > relationship. > > My questions are related to SQL Alchemy ORM concepts: > 1) Relationships > 2) Association Object pattern > 3) Association Proxy > > > To help me grasp the concepts, I pieced together a working example of an M > to N relation and drew a diagram showing the relationships. The scenario > is of a very crude appointment scheduler that someone like a realtor may > use to keep track of who is visiting what property. My attribute naming > convention was chosen to facilitate our discussion. *Link: Github repo > <http://www.github.com/dowwie/sqlalchemyillustrated>* > > There are two files of interest: > > - orm_associations.py -- a working example > - "SQLAlchemy - Association Object Relations.pdf" -- contains a > diagram of the M to N relationship in orm_associations.py > > > In this example, a user can be added to a meeting OR a meeting can be > added to a user using either of these association proxies: > > Meeting.attendees_proxy.append(User) > or > User.meetings_proxy.append(Meeting) > > These statements create the desired outcome-- a new Appointment record > inserted into the association table and possibly a new user or meeting > record if none already exist. > > I'd like to know what exactly is happening in the ORM when either of these > statements is executed. > For instance, what is the association_proxy creator doing? If I add a > user to a meeting, the attendees_proxy creator is defined as follows: > creator=lambda user: Appointment(appointment_user_relation=user)) > The creator expression appears to be creating a new Appointment object, > but then defines the RELATIONSHIP as a User object? I'm missing something > here. No idea what is going on. It seems to be all a bit to automagical > to me. > > > Thanks > > Darin > > -- 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.
