if there are no dependencies between two particular objects of different classes, say A and B, then there is no deterministic ordering between them. For objects of the same class, they are inserted in the order in which they were added to the Session.
the correct way to solve this problem in SQLAlchemy is to use relationship() fully. I know you've stated that these objects have a relationship() between them but you have to actually use it, that is: obj_a = A() obj_b = B() obj_a.some_relationship = obj_b # will definitely flush correctly unless there is a bug OTOH if you are only using foreign key attributes, the ORM does *not* have any idea in how it should be flushing these: obj_a = A() obj_b = B() obj_a.some_fk = obj_b.some_id # ORM doesn't care about this, no ordering is implied since you said you're not setting any IDs, I'm not sure how you could be doing the above. On Tue, Sep 18, 2018 at 5:53 AM Simon King <si...@simonking.org.uk> wrote: > > It's not something I've ever looked into, but I'm not aware of any > debugging options here, no. You'd probably want to start by scattering > print statements around the UOWTransaction class > (https://bitbucket.org/zzzeek/sqlalchemy/src/c94d67892e68ac317d72eb202cca427084b3ca74/lib/sqlalchemy/orm/unitofwork.py?at=master&fileviewer=file-view-default#unitofwork.py-111) > > Looking at that code made me wonder whether you've set any particular > cascade options on your relationship; I'm not sure if cascade options > affect the dependency calculation. > > Simon > > On Tue, Sep 18, 2018 at 5:28 AM Alex Rothberg <agrothb...@gmail.com> wrote: > > > > In order to guide me in stripping down this code to produce an example for > > positing, are there any options / flags / introspections I can turn on to > > understand how sql makes decisions about the order in which is writes > > statements to the DB? > > > > On Friday, September 14, 2018 at 10:13:45 AM UTC-4, Simon King wrote: > >> > >> In that case can you show us the code that is causing the problem? > >> On Fri, Sep 14, 2018 at 2:55 PM Alex Rothberg <agrot...@gmail.com> wrote: > >> > > >> > I am not generating any IDs myself and I already have relationships > >> > between the models. > >> > > >> > On Friday, September 14, 2018 at 4:33:08 AM UTC-4, Simon King wrote: > >> >> > >> >> On Thu, Sep 13, 2018 at 10:50 PM Alex Rothberg <agrot...@gmail.com> > >> >> wrote: > >> >> > > >> >> > Is it possible to hint at sqla the order in which it should write out > >> >> > changes to the DB? > >> >> > > >> >> > I am having issues in which I add two new objects to a session, a and > >> >> > b where a depends on b, but sqla is flushing a before b leading to an > >> >> > fk issue. I can solve this a few ways: explicitly calling flush after > >> >> > adding b, or changing the fk constraint to be initially deferred. > >> >> > Ideally I would not have to do either of these. > >> >> > > >> >> > >> >> If you have configured a relationship between the two classes > >> >> (http://docs.sqlalchemy.org/en/latest/orm/tutorial.html#building-a-relationship), > >> >> and you've linked the objects together using that relationship (a.b = > >> >> b), then SQLAlchemy will flush them in the correct order. If you are > >> >> generating your IDs in Python and assigning them to the primary and > >> >> foreign key columns directly, SQLAlchemy probably won't understand the > >> >> dependency. > >> >> > >> >> Does using a relationship fix your problem? > >> >> > >> >> Simon > >> > > >> > -- > >> > 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. > >> > --- > >> > 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. > >> > To post to this group, send email to sqlal...@googlegroups.com. > >> > Visit this group at https://groups.google.com/group/sqlalchemy. > >> > For more options, visit https://groups.google.com/d/optout. > > > > -- > > 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. > > --- > > 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 https://groups.google.com/group/sqlalchemy. > > For more options, visit https://groups.google.com/d/optout. > > -- > 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. > --- > 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 https://groups.google.com/group/sqlalchemy. > For more options, visit https://groups.google.com/d/optout. -- 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. --- 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. 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