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? 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/
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