Issue 1:
Migrated issue, originally created by Bertrand Croq (@bcroq)

Upgrading from SQLAlchemy 1.0.9 to 1.0.10 breaks the following code:

from sqlalchemy import create_engine
from sqlalchemy import Column, ForeignKey, Integer, String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship, sessionmaker

Base = declarative_base()

class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)

class UserRole(Base):
__tablename__ = 'user_roles'

id = Column(Integer, primary_key=True)

row_type = Column(String, nullable=False)
__mapper_args__ = {'polymorphic_on': row_type}

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

class Admin(UserRole):
__tablename__ = 'admins'
__mapper_args__ = {'polymorphic_identity': 'admin'}

id = Column(Integer, ForeignKey('user_roles.id'), primary_key=True)

class Thing(Base):
__tablename__ = 'things'

id = Column(Integer, primary_key=True)

admin_id = Column(Integer, ForeignKey('admins.id'))
admin = relationship('Admin', lazy=False)

engine = create_engine('sqlite:///:memory:', echo=True)
Session = sessionmaker(bind=engine)
Base.metadata.create_all(engine)

session = Session()
print session.query(Thing).all()

Issue 2:
Migrated issue, originally created by Bastien Chatelard (@bchatelard)

I am facing a regression on joinedload on polymorphic entity in 1.0.10.

I have reproduced a minimal test case that works fine in 1.0.9 and does not in 1.0.10:

import sqlalchemy as sa
import sqlalchemy.orm
from sqlalchemy.orm import joinedload
import sqlalchemy.ext.declarative
import sqlalchemy.ext.orderinglist

Base = sqlalchemy.ext.declarative.declarative_base()

class Person(Base):
__tablename__ = 'person'

id = sa.Column(sa.Integer, nullable=False, primary_key=True)
person_type = sa.Column(sa.String(20), nullable=False)

__mapper_args__ = {
'polymorphic_on': person_type,
'with_polymorphic': '*',
}

class User(Person):
__mapper_args__ = {'polymorphic_identity': 'user'}

class Admin(Person):
__mapper_args__ = {'polymorphic_identity': 'admin'}

class Action(Base):
__tablename__ = 'action'
id = sa.Column(sa.Integer, nullable=False, primary_key=True)

author_id = sa.Column(sa.Integer, sa.ForeignKey(User.id))
author = sa.orm.relationship('User')

post_type = sa.Column(sa.String(20), nullable=False)

__mapper_args__ = {
'polymorphic_on': post_type,
'polymorphic_identity': 'post',
'with_polymorphic': '*',
}

class Like(Action):
__tablename__ = 'like'
__mapper_args__ = {'polymorphic_identity': 'like'}
id = sa.Column(sa.Integer, sa.ForeignKey('action.id'), primary_key=True)

class Comment(Action):
__tablename__ = 'comment'
__mapper_args__ = {'polymorphic_identity': 'comment'}
id = sa.Column(sa.Integer, sa.ForeignKey('action.id'), primary_key=True)

article_id = sa.Column(sa.Integer, sa.ForeignKey('article.id'))
article = sa.orm.relationship('Article', primaryjoin='Article.id==Comment.article_id', backref='comments')

class Article(Base):
__tablename__ = 'article'
id = sa.Column(sa.Integer, nullable=False, primary_key=True)

engine = sa.create_engine('sqlite:///:memory:', echo=True)

Base.metadata.drop_all(engine)
Base.metadata.create_all(engine)

Session = sa.orm.sessionmaker(bind=engine)
session = Session()

user1 = User(id=1)
admin1 = Admin(id=2)
user2 = User(id=3)
article1 = Article(id=1)
comment1 = Comment(id=2, author=user1, article_id=1)
comment2 = Comment(id=3, author=user2, article_id=1)

session.add_all([user1, user2, admin1, article1, comment1, comment2])
session.commit()
session.expunge_all()

# Works with 1.0.9
# Not working with 1.0.10: raise AssertionError
try:
new_n1 = session.query(Article).options(
joinedload(Article.comments).joinedload(Action.author),
).all()

print new_n1
print new_n1[0].comments
print new_n1[0].comments[0].author
except AssertionError as e:
print e

# Works with 1.0.9
# Not working with 1.0.10: 2 queries
try:
new_n1 = session.query(Article).options(
joinedload('comments'),
joinedload('comments.author')
).all()

print new_n1
print new_n1[0].comments
print new_n1[0].comments[0].author
except AssertionError as e:
print e

# Works with 1.0.9
# Not working with 1.0.10: raise AssertionError
try:
new_n1 = session.query(Article).options(
joinedload('comments').joinedload('author')
).all()

print new_n1
print new_n1[0].comments
print new_n1[0].comments[0].author
except AssertionError as e:
print e

# Works with 1.0.9
# Not working with 1.0.10: raise AssertionError
try:
new_n1 = session.query(Article).options(
joinedload('comments').load_only('id', 'author_id').joinedload('author').load_only('id')
).all()

print new_n1
print new_n1[0].comments
print new_n1[0].comments[0].author
except AssertionError as e:
print e

It might be related to #2714 or #3593