Load options aren't looking at the superclass

[sqlalchemy-bot]

Migrated issue, originally created by malthe (@malthe)

If a query is made on an alias then the load_only option fails to exclude properties that are set on a base class of the aliased mapper.

q = sess.query(alias).options(load_only("age"))

This is demonstrated in a test case here: https://github.com/malthe/sqlalchemy/tree/load-only-with-alias-issue

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

likely not a bug, you should be using load_only(alias.age). please confirm.

[sqlalchemy-bot]

malthe (@malthe) wrote:

Actually I failed to reproduce the actual problem in this test case.

But there is an issue which is that the alias results in a subselect that lists all the columns in the mapper even though they're not part of the column selection:

select a, b from (select a, b, c from foo join bar on ...)

Note how c is not in the result, but it's still being listed in the subselect.

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

it's time to provide a real test case :). Here's a start:

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)


e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)

s = Session(e)

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

oh, does your test case show this? I can look there.

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

hm, I see a fork of SQLAlchemy there. just give me a quick .py script, thanks.

[sqlalchemy-bot]

malthe (@malthe) wrote:

yeah here's the diff: malthe@dcd43de

I thought I'd write a test case against the code base.

I run the test via:

./sqla_nose.py -sxv -w orm/test_deferred.py

But I can try and isolate to a simple .py file.

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

OK, those tests can be helpful when I put the fix in but I need to understand the issue first (I'm fixing something else right now).

[sqlalchemy-bot]

malthe (@malthe) wrote:

Here's a snippet that does demonstrate the issue:

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class A(Base):
    __tablename__ = 'a'

    id = Column(Integer, primary_key=True)
    a_name = Column(String)


class B(A):
    __tablename__ = 'b'

    id = Column(Integer, ForeignKey("a.id"), primary_key=True)
    b_name = Column(String)


class C(Base):
    __tablename__ = 'c'

    id = Column(Integer, primary_key=True)
    c_name = Column(String)
    b_id = Column("b_id", Integer, ForeignKey("b.id"))

    b = relationship(B)

e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)

s = Session(e)

b = B(id=1, a_name="foo", b_name="bar")
s.add(b)

c = C(id=1, b_id=b.id, c_name="boo")
s.add(c)

s.flush()

print s.query(C).join(B).options(
    contains_eager(C.b).load_only("id")
)

Note how a.a_name is included, but b.b_name is correctly excluded.

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

ok, so is this the bug?

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class A(Base):
    __tablename__ = 'a'

    id = Column(Integer, primary_key=True)
    a_name = Column(String)

class B(A):
    __tablename__ = 'b'

    id = Column(Integer, ForeignKey("a.id"), primary_key=True)
    b_name = Column(String)


s = Session()

print s.query(B).options(load_only(B.id))

it isn't looking at the superclass. can we rename this issue then? This is all I'm looking at so far.

SELECT b.id AS b_id, a.id AS a_id, a.a_name AS a_a_name 
FROM a JOIN b ON a.id = b.id

[sqlalchemy-bot]

malthe (@malthe) wrote:

I think that's the bug. Let me rename the issue.

[sqlalchemy-bot]

Changes by malthe (@malthe):

• changed title from "Load options ignore inherited classes with alias" to "Load options aren't looking at the superclass"

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

• The "wildcard" loader options, in particular the one set up by
  the :func:.orm.load_only option to cover all attributes not
  explicitly mentioned, now takes into account the superclasses
  of a given entity, if that entity is mapped with inheritance mapping,
  so that attribute names within the superclasses are also omitted
  from the load. Additionally, the polymorphic discriminator column
  is unconditionally included in the list, just in the same way that
  primary key columns are, so that even with load_only() set up,
  polymorphic loading of subtypes continues to function correctly.
  fixes Load options aren't looking at the superclass #3287

→ b63aae2

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

• The "wildcard" loader options, in particular the one set up by
  the :func:.orm.load_only option to cover all attributes not
  explicitly mentioned, now takes into account the superclasses
  of a given entity, if that entity is mapped with inheritance mapping,
  so that attribute names within the superclasses are also omitted
  from the load. Additionally, the polymorphic discriminator column
  is unconditionally included in the list, just in the same way that
  primary key columns are, so that even with load_only() set up,
  polymorphic loading of subtypes continues to function correctly.
  fixes Load options aren't looking at the superclass #3287

(cherry picked from commit b63aae2)

Conflicts:
lib/sqlalchemy/orm/mapper.py

→ 11383da

[sqlalchemy-bot]

Changes by Michael Bayer (@zzzeek):

• changed status to closed

[sqlalchemy-bot]

malthe (@malthe) wrote:

This solves the problem.