[Sqlalchemy-tickets] Issue #3037: support setting load options on instances (zzzeek/sqlalchemy)

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

New issue 3037: support setting load options on instances
https://bitbucket.org/zzzeek/sqlalchemy/issue/3037/support-setting-load-options-on-instances

Mike Bayer:

proof of concept


```
#!python

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)
    bs = relationship("B")

class B(Base):
    __tablename__ = 'b'

    id = Column(Integer, primary_key=True)
    a_id = Column(Integer, ForeignKey('a.id'))
    cs = relationship("C")

class C(Base):
    __tablename__ = 'c'

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

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

sess = Session(e)
sess.add_all([
    A(bs=[
        B(cs=[C(), C()]),
        B(cs=[C(), C()])
    ])
])
sess.commit()

a1 = sess.query(A).first()
inspect(a1).load_options = inspect(a1).load_options.union([joinedload(B.cs)])

for b in a1.bs:
    print b.cs

```

im not sure why the above option doesn't have to mention "A.bs" at all, there should be some path logic taking this into account.  The public API should be:

    inspect(a1).set_load_option("bs", joinedload(...))