On Fri, Jan 24, 2014 at 4:22 PM, Simon King <[email protected]> wrote:
> Hi again,
>
> While testing the complicated relationship from the other thread, I
> noticed that I was generating a lot of queries that I couldn't
> immediately explain. After a bit of digging, it turned out that it was
> due to my use of code based on the "versioned objects" example at
> http://docs.sqlalchemy.org/en/rel_0_9/_modules/examples/versioned_history/history_meta.html.
>
> In the test script below we have 3 classes. Users belong to Companies,
> and Companies reference a single Terms row. In the example, only the
> Company class is versioned.
>
> The test script inserts a single user, company and terms row, then in
> new transaction loads the company and adds a new user. If you look at
> the SQL output, you should see that it loads the company.terms
> relationship, which doesn't seem like it should be necessary.
>
> I think it's due to the following code from history_meta.py:
>
> if not obj_changed:
> # not changed, but we have relationships. OK
> # check those too
> for prop in obj_mapper.iterate_properties:
> if isinstance(prop, RelationshipProperty) and \
> attributes.get_history(obj, prop.key).has_changes():
> for p in prop.local_columns:
> if p.foreign_keys:
> obj_changed = True
> break
> if obj_changed is True:
> break
>
> I can't figure out the circumstances when this should be necessary -
> can someone explain it to me?
>
> Thanks a lot,
>
> Simon
Doh, forgot the test script:
import sqlalchemy as sa
import sqlalchemy.orm as saorm
from sqlalchemy.ext.declarative import declarative_base
from history_meta import Versioned, versioned_session
Base = declarative_base()
class Terms(Base):
__tablename__ = 'terms'
id = sa.Column(sa.Integer(), primary_key=True)
version = sa.Column(sa.Integer(), default=1)
terms = sa.Column(sa.UnicodeText())
class Company(Versioned, Base):
__tablename__ = 'company'
id = sa.Column(sa.Integer(), primary_key=True)
name = sa.Column(sa.Unicode(60))
termsid = sa.Column(sa.Integer, sa.ForeignKey(Terms.id),
nullable=False)
terms = saorm.relationship(Terms)
class User(Base):
__tablename__ = 'user'
id = sa.Column(sa.Integer(), primary_key=True)
name = sa.Column(sa.Unicode(60))
companyid = sa.Column(sa.Integer, sa.ForeignKey(Company.id),
nullable=False)
company = saorm.relationship(Company, backref='members')
def test():
engine = sa.create_engine('sqlite:///:memory:', echo=True)
Session = saorm.sessionmaker(bind=engine)
versioned_session(Session)
Base.metadata.create_all(engine)
session = Session()
session.add(
User(name='Simon',
company=Company(name='whatever',
terms=Terms(version=1))
)
)
session.commit()
company = session.query(Company).first()
u = User(name='Larry', company=company)
session.add(u)
print '\n\n' + '#' * 70 + '\n'
session.flush()
if __name__ == '__main__':
test()
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