Hi *,
a while ago I noticed a small problem with SQLAlchemy. I was able to
work around this, but I am still wondering if this should be required.
I am doing synchronization between multiple databases (think distributed
VCS). Basically, each outdated object on the receiving side is updated
by updating its variables and committing it to the database.
Now there is some required information in those objects which is checked
in the __init__ method of each class. Therefore to create an object from
the remote object, I am skipping the call to __init__ (like e.g. pickle
does).
(Interestingly, pickle creates an empty class first and goes to update
__class__ afterwards. Why?!)
So to create the instances for the mapped objects, I used
instance = MyClass.__new__(MyClass)
as in the attached example. This fails with an attribute error for
"_sa_instance_state". My work around is to use
instance = manager_of_class(MyClass).new_instance()
but I am wondering if this should be needed, especially since the
ClassManager class is not documented. What should I be using instead?
Greetings, Torsten
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from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.orm.attributes import manager_of_class
metadata = MetaData()
class Base(object): pass
base_table = Table("base", metadata,
Column("id", Integer, primary_key=True),
Column("name", String))
mapper(Base, base_table)
b = Base()
assert b.name is None
b = manager_of_class(Base).new_instance()
b.name = "using manager_of_class"
b = Base.__new__(Base)
b.name = "using __new__"
