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 description.
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