On Wed, Nov 29, 2017 at 3:32 PM, Jonathan Vanasco <jonat...@findmeon.com> wrote:
> I have a potential relationship between Foo and Bar that is defined as
> follows, and has usually been read-only from legacy data.
>
> All the code works, I just want to make sure I'm handling this case in a
> clear and concise way.
>
> I've (over)simplified the case down to this:
>
> class Foo(Base):
> __tablename__ = 'foo'
> id = Column(Integer, primary_key=True)
> name = Column(Unicode(6), nullable=False)
>
> bar = relationship("Bar",
> primaryjoin="Foo.id==Bar.id__foo",
> uselist=False,
> back_populates='foo',
> )
>
> class Bar(Base):
> __tablename__ = 'bar'
> id = Column(Integer, primary_key=True)
> name = Column(Unicode(6), nullable=False)
> id__foo = Column(Integer, ForeignKey("foo.id"), nullable=True, )
>
> foo = relationship("Foo",
> primaryjoin="Bar.id__foo==Foo.id",
> uselist=False,
> back_populates='bar',
> )
>
>
> In a current feature ticket, I'm in a situation where I need to upgrade an
> instance of Foo with an instance Bar and dealing with some get/create
> functions that do their own flushes. That block of code basically looks
> like this:
>
> def getcreate_bar(bar_name, foo=None):
> b = s.query(Bar).filter(Bar.name==bar_name).first()
> if not b:
> b = Bar()
> b.name = bar_name
> b.id__foo = foo.id if foo else None
> s.add(b)
> s.flush(objects=[b, ])
> return b
>
> foo = s.query(Foo).get(1)
> if not foo.bar:
> bar = getcreate_bar(bar_name, foo)
> foo.bar = bar # attribute needed for additional work
> s.flush(objects=[foo, ]) # flush only needed if bar isn't new
>
>
> my question covers where I create the `bar` and make it instantly available
> as a foo attribute. Is there a better way to handle this or make it more
> readable?
One way would be to make a @property or hybrid that generates it, but
maybe you want to try this new event:
http://docs.sqlalchemy.org/en/latest/orm/events.html?highlight=init_scalar#sqlalchemy.orm.events.AttributeEvents.init_scalar
it's probably only tested for scalar values but in theory should work
for objects too. But you'd be testing that that actually works b.c.
I'm not sure.
If I create a new foo, the flush of `foo` doesn't emit SQL after
> sqlalchemy decides it doesn't have to. I do need that flush if I already
> had bar, but it wasn't associated to foo.
>
>
>
> --
> 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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