In looking at what you wrote doesn't this cause an fk violation (it does
for me):
2018-10-08 10:18:38,760 INFO sqlalchemy.engine.base.Engine INSERT INTO
employee (title_id, department_id, fund_id) VALUES (%(title_id)s,
%(department_id)s, %(fund_id)s) RETURNING employee.id
2018-10-08 10:18:38,763 INFO sqlalchemy.engine.base.Engine INSERT INTO
fund_title (title_id, department_id, fund_id) VALUES (%(title_id)s,
%(department_id)s, %(fund_id)s) RETURNING fund_title.id
in that a a (non deferred) fk is violated between employee and fund_title ?
On Mon, Oct 8, 2018 at 10:20 AM Mike Bayer <mike...@zzzcomputing.com> wrote:
> On Sun, Oct 7, 2018 at 7:11 PM Alex Rothberg <agrothb...@gmail.com> wrote:
> >
> > Okay so I investigated / thought about this further. The issue is that
> while I do have a relationship between the various models, some of the
> relationships are viewonly since I have overlapping fks.
> >
> > For example I have a model Employee, which has fks: department_id,
> title_id, and fund_id. The related models are Department (fk
> department_id), Title (fk department_id and title_id) , Fund (fk fund_id)
> and FundTitle (fk department_id, title_id and fund_id). I have set
> FundTitle to viewonly. When updating / creating an Employee, I do create
> and add a new FundTitle to the session, however I don't assign it to the
> employee as the relationship is viewonly. If I don't flush before making
> the assignment, the final flush / commit attempts to update / create the
> employee before creating the FundTitle.
>
> let's work with source code that is runnable (e.g. MCVE). Below is
> the model that it seems you are describing, and then there's a
> demonstration of assembly of all those components using relationships,
> a single flush and it all goes in in the correct order, all FKs are
> nullable=False.
>
> from sqlalchemy import *
> from sqlalchemy.orm import *
> from sqlalchemy.ext.declarative import declarative_base
>
> Base = declarative_base()
>
>
> class Employee(Base):
> __tablename__ = 'employee'
> id = Column(Integer, primary_key=True)
> title_id = Column(ForeignKey('title.id'), nullable=False)
> department_id = Column(ForeignKey('department.id'), nullable=False)
> fund_id = Column(ForeignKey('fund.id'), nullable=False)
> department = relationship("Department")
> title = relationship("Title")
> fund = relationship("Fund")
>
>
> class Title(Base):
> __tablename__ = 'title'
> id = Column(Integer, primary_key=True)
> department_id = Column(ForeignKey('department.id'), nullable=False)
> department = relationship("Department")
>
>
> class Department(Base):
> __tablename__ = 'department'
> id = Column(Integer, primary_key=True)
>
>
> class Fund(Base):
> __tablename__ = 'fund'
> id = Column(Integer, primary_key=True)
> title_id = Column(ForeignKey('title.id'), nullable=False)
> department_id = Column(ForeignKey('department.id'), nullable=False)
> department = relationship("Department")
> title = relationship("Title")
>
>
> class FundTitle(Base):
> __tablename__ = 'fund_title'
> id = Column(Integer, primary_key=True)
> title_id = Column(ForeignKey('title.id'), nullable=False)
> department_id = Column(ForeignKey('department.id'), nullable=False)
> fund_id = Column(ForeignKey('fund.id'), nullable=False)
> department = relationship("Department")
> title = relationship("Title")
> fund = relationship("Fund")
>
> e = create_engine("postgresql://scott:tiger@localhost/test", echo=True)
> Base.metadata.create_all(e)
>
> s = Session(e)
>
> d1 = Department()
> t1 = Title(department=d1)
> f1 = Fund(department=d1, title=t1)
> ft1 = FundTitle(title=t1, department=d1, fund=f1)
> e1 = Employee(title=t1, department=d1, fund=f1)
>
> s.add_all([d1, t1, f1, ft1, e1])
> s.commit()
>
>
> the INSERTs can be ordered naturally here and the unit of work will do
> that for you if you use relationship:
>
> BEGIN (implicit)
> 2018-10-08 10:18:38,750 INFO sqlalchemy.engine.base.Engine INSERT INTO
> department DEFAULT VALUES RETURNING department.id
> 2018-10-08 10:18:38,750 INFO sqlalchemy.engine.base.Engine {}
> 2018-10-08 10:18:38,753 INFO sqlalchemy.engine.base.Engine INSERT INTO
> title (department_id) VALUES (%(department_id)s) RETURNING title.id
> 2018-10-08 10:18:38,753 INFO sqlalchemy.engine.base.Engine
> {'department_id': 1}
> 2018-10-08 10:18:38,757 INFO sqlalchemy.engine.base.Engine INSERT INTO
> fund (title_id, department_id) VALUES (%(title_id)s,
> %(department_id)s) RETURNING fund.id
> 2018-10-08 10:18:38,757 INFO sqlalchemy.engine.base.Engine
> {'title_id': 1, 'department_id': 1}
> 2018-10-08 10:18:38,760 INFO sqlalchemy.engine.base.Engine INSERT INTO
> employee (title_id, department_id, fund_id) VALUES (%(title_id)s,
> %(department_id)s, %(fund_id)s) RETURNING employee.id
> 2018-10-08 10:18:38,761 INFO sqlalchemy.engine.base.Engine
> {'title_id': 1, 'department_id': 1, 'fund_id': 1}
> 2018-10-08 10:18:38,763 INFO sqlalchemy.engine.base.Engine INSERT INTO
> fund_title (title_id, department_id, fund_id) VALUES (%(title_id)s,
> %(department_id)s, %(fund_id)s) RETURNING fund_title.id
> 2018-10-08 10:18:38,764 INFO sqlalchemy.engine.base.Engine
> {'title_id': 1, 'department_id': 1, 'fund_id': 1}
> 2018-10-08 10:18:38,766 INFO sqlalchemy.engine.base.Engine COMMIT
>
>
>
>
>
> >
> > On Tuesday, September 18, 2018 at 9:02:30 AM UTC-4, Mike Bayer wrote:
> >>
> >> 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 <agrot...@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.
> >> > >> > ---
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> >> > >
> >> > > --
> >> > > 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.
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> >> >
> >> > --
> >> > 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.
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> >
> > --
> > 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.
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> --
> 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
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--
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.
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