> On Feb 27, 2015, at 4:48 PM, Eric Smith <e...@esmithy.net> wrote:
>
> To those more experienced than me, does this behavior make sense? If so,
> could you further my education with an explanation?
>
> If I change an attribute, is_modified returns True (as expected).
> If I then reference a relationship, is_modified returns False (unexpected).
>
> My output for the following program (using SQLAlchemy 0.9.7) is:
>
> False
> True
> False
>
> Thanks,
> Eric
>
>
> from sqlalchemy import Column, Integer, String, create_engine, ForeignKey
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.orm import sessionmaker, relationship
>
>
> Base = declarative_base()
>
>
> class Parent(Base):
> __tablename__ = 'parent'
> id = Column(Integer, primary_key=True, nullable=False)
> message = Column(String)
> children = relationship("Child", backref='parent')
>
>
> class Child(Base):
> __tablename__ = 'child'
> id = Column(Integer, primary_key=True, nullable=False)
> parent_id = Column(Integer, ForeignKey('parent.id'))
>
>
> def main():
> engine = create_engine('sqlite:///:memory:')
> Session = sessionmaker(bind=engine)
> Base.metadata.create_all(engine)
>
> db = Session()
> parent = Parent()
> db.add(parent)
> db.commit()
>
> print db.is_modified(parent)
> parent.message = "hi"
> print db.is_modified(parent)
> len(parent.children) # Should this change is_modified?
> print db.is_modified(parent)
Turn on sql echoing, which is always the first step towards understanding ORM
behavior, and you'll see that the call to parent.children invokes a lazy load
operation, which is a Query hence it autoflushes first, thereby synchronizing
the state of "message" and resetting the modified flag.
>
> if __name__ == '__main__':
> main()
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