SQLAlchemy: Disable lazy loading and load object only on join()

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I'm working on disabling lazy loading on SQLAlchemy, so it will not load by default all the objects when fetching the records from the database. I'm trying to load for example the user object only from the event object when you specifically join it on the query or if you access it for example event.user. Is this possible somehow with a parameter or is it a bad practice to disabling lazy loading?

I already tried the noload("*") but it disables any join at the end. For example I have the below model and also the queries which I'm doing my tests.

# Event model
class Event(Base):
    __tablename__ = 'events'

    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String(50), nullable=False)
    amount = Column(Integer)

    _user_id = Column("user_id", Integer, ForeignKey("users.id"), nullable=False)
    user = relationship(User)

# Query - This fetches also the whole user object <-- I don't want such behavior
some_session.query(Event).all()

# Query - I would like to load the user object when I will use the join() if possible
some_session.query(Event).join(Event.user).all()

enter image description here

sqlalchemy python
1 Answers

The default relationship loading strategy is "lazy loading", which works the way you want; the related User is loaded only if the user attribute of an Event object is touched. In your case it is touched by your IDE, when it inspects the object in order to display the attributes as a handy tree, and that triggers the fetch. The same happens easily with custom __repr__() implementations, if not careful.

When you wish to eager load the related users using a join, either use joined loading:

some_session.query(Event).options(joinedload(Event.user)).all()

or if you wish to filter based on User in the same query, explicit join(s) and contains_eager():

some_session.query(Event).join(Event.user).options(contains_eager(Event.user)).all()
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