Can SQLAlchemy eager/joined loads be suppressed once set up?

You can use Query.options(raiseload('*')) or Query.enable_eagerloads(False).

Query.enable_eagerloads(False) will disable all eager loading on the query. That is, even if you put a joinedload() or something, it won't be executed.

Query.options(raiseload('*')) will install a raiseload loader on every column, making sure they're not lazily loaded: an exception is raised instead. Note that this mode is fine for development and testing environments, but may be destructive in production. Make it optional like this:

Query.options(raiseload('*') if development else defaultload([]))

also note that raiseload('*') only works for top-level relationships. It won't spread on joined entities! If you request a relationship, you have to specify it twice:

session.query(User).options(
    load_only('id'),
    joinedload(User.addresses).options(
        load_only('id'),
        raiseload('*')
    ),
    raiseload('*')
)

also, raiseload('*') only works for relationships, not columns :) For columns, use defer(..., raiseload=True)

You may override eagerness of properties on query-by-query basis, as far as I remember. Will this work?

from sqlalchemy.orm import lazyload
joe = (s2.query(User)
    .options(lazyload('addresses'))
    .filter_by(name = "Joe").one())
for addr in joe.addresses:
    print addr.address

See the docs.