[Sqlalchemy-tickets] Issue #4084: make_transient_to_pending expires deferred attrs making them load on refresh (zzzeek/sqlalchemy)

[Michael B. <iss...@bi...>]

New issue 4084: make_transient_to_pending expires deferred attrs making them load on refresh
https://bitbucket.org/zzzeek/sqlalchemy/issues/4084/make_transient_to_pending-expires-deferred

Michael Bayer:

```
#!python

from sqlalchemy import Column, Integer, String, create_engine
from sqlalchemy.orm import Session, deferred
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm.session import make_transient_to_detached


Base = declarative_base()


class MyTable(Base):
    __tablename__ = 'my_table'

    id = Column(Integer, primary_key=True)
    undeferred = Column(String)
    deferred_column = deferred(Column(String))

e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
e.execute(
    "insert into my_table (id, undeferred, "
    "deferred_column) values (1, 'foo', 'bar')")

s = Session(e)


def expire_via_detached():
    item = MyTable(id=1)

    make_transient_to_detached(item)
    s.add(item)
    item.undeferred
    assert 'deferred_column' not in item.__dict__
    s.close()


def expire_normally():
    item = s.query(MyTable).first()
    s.expire(item)
    item.undeferred
    assert 'deferred_column' not in item.__dict__
    s.close()


def expire_explicit_attrs():
    item = s.query(MyTable).first()
    s.expire(item, ['undeferred', 'deferred_column'])
    item.undeferred
    assert 'deferred_column' in item.__dict__
    s.close()

expire_normally()
expire_explicit_attrs()
expire_via_detached()

```

this is due to state._expire(state, state.unloaded) in make_transient_to_pending(). When a deferred attribute is explicitly expired, it becomes part of the next full load.