[Sqlalchemy-tickets] Issue #4049: cache key error w/ undefer group on top of defaultload, 1.2 regression w/ lazyload caching (zzzeek/sqlalchemy)

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

New issue 4049: cache key error w/ undefer group on top of defaultload, 1.2 regression w/ lazyload caching
https://bitbucket.org/zzzeek/sqlalchemy/issues/4049/cache-key-error-w-undefer-group-on-top-of

Michael Bayer:

related to #4048, we can't even get to the lazyload for this one

```
#!python


    def test_undefer_group_from_relationship_lazyload(self):
        users, Order, User, orders = \
            (self.tables.users,
             self.classes.Order,
             self.classes.User,
             self.tables.orders)

        mapper(User, users, properties=dict(
            orders=relationship(Order, order_by=orders.c.id)))
        mapper(
            Order, orders, properties=util.OrderedDict([
                ('userident', deferred(orders.c.user_id, group='primary')),
                ('description', deferred(orders.c.description,
                 group='primary')),
                ('opened', deferred(orders.c.isopen, group='primary'))
            ])
        )

        sess = create_session()
        q = sess.query(User).filter(User.id == 7).options(
            defaultload(User.orders).undefer_group('primary')
        )

        def go():
            result = q.all()
            o2 = result[0].orders[1]
            eq_(o2.opened, 1)
            eq_(o2.userident, 7)
            eq_(o2.description, 'order 3')
        self.assert_sql_count(testing.db, go, 1)

```

trace:

```
#!


Traceback (most recent call last):
  File "/home/classic/dev/sqlalchemy/test/orm/test_deferred.py", line 419, in test_undefer_group_from_relationship_lazyload
    self.assert_sql_count(testing.db, go, 1)
  File "/home/classic/dev/sqlalchemy/test/../lib/sqlalchemy/testing/assertions.py", line 520, in assert_sql_count
    db, callable_, assertsql.CountStatements(count))
  File "/home/classic/dev/sqlalchemy/test/../lib/sqlalchemy/testing/assertions.py", line 500, in assert_sql_execution
    result = callable_()
  File "/home/classic/dev/sqlalchemy/test/orm/test_deferred.py", line 415, in go
    o2 = result[0].orders[1]
  File "/home/classic/dev/sqlalchemy/test/../lib/sqlalchemy/orm/attributes.py", line 242, in __get__
    return self.impl.get(instance_state(instance), dict_)
  File "/home/classic/dev/sqlalchemy/test/../lib/sqlalchemy/orm/attributes.py", line 603, in get
    value = self.callable_(state, passive)
  File "/home/classic/dev/sqlalchemy/test/../lib/sqlalchemy/orm/strategies.py", line 623, in _load_for_state
    return self._emit_lazyload(session, state, ident_key, passive)
  File "<string>", line 1, in <lambda>
  File "/home/classic/dev/sqlalchemy/test/../lib/sqlalchemy/orm/strategies.py", line 714, in _emit_lazyload
    state.load_options, effective_path
  File "/home/classic/dev/sqlalchemy/test/../lib/sqlalchemy/ext/baked.py", line 178, in _add_lazyload_options
    cache_key = opt._generate_cache_key(cache_path)
  File "/home/classic/dev/sqlalchemy/test/../lib/sqlalchemy/orm/strategy_options.py", line 389, in _generate_cache_key
    c_key = opt._generate_cache_key(path)
  File "/home/classic/dev/sqlalchemy/test/../lib/sqlalchemy/orm/strategy_options.py", line 113, in _generate_cache_key
    obj.strategy +
TypeError: can only concatenate tuple (not "NoneType") to tuple

```