On Oct 16, 2010, at 4:02 PM, Michael Hipp wrote:
> On 10/16/2010 1:55 PM, Michael Bayer wrote:
>>
>> On Oct 16, 2010, at 2:03 PM, Michael Hipp wrote:
>>
>>> On 10/16/2010 12:52 PM, Michael Bayer wrote:
>>>>
>>>> On Oct 16, 2010, at 1:02 PM, Michael Hipp wrote:
>>>>
>>>>> On 8/24/2010 9:47 PM, Michael Bayer wrote:
>>>>>> Michael Hipp wrote:
>>>>>>> How do I make a copy of an orm object such that modifications to the
>>>>>>> copy do not affect the original?
>>>>>>
>>>>>> The mapped object has a member "_sa_instance_state" that you basically
>>>>>> don't want to transfer to your new object. You want it to have its own
>>>>>> "_sa_instance_state" and this comes from calling the plain constructor,
>>>>>> which the "copy" module, if that's what you're using, does not use. You
>>>>>> also want to set attributes normally, not populating __dict__ directly.
>>>>>> So just basically don't use the "copy" module.
>>>>>>
>>>>>> x = MyObject()
>>>>>> for a in dir(myoldobject):
>>>>>> if not a.startswith('_'):
>>>>>> setattr(x, a, getattr(myoldobject, a))
>>>>>
>>>>> Resurrecting an old thread ...
>>>>>
>>>>> I'm just now getting around to try this but I'm finding out it doesn't
>>>>> really work like I'd hoped.
>>>>>
>>>>> As soon as 'getattr' hits a column with a ForeignKey it immediately tries
>>>>> to autoflush INSERT 'x'. But 'x' is only half-baked and not ready to be
>>>>> saved.
>>>>>
>>>>> In fact, I don't ever want to save 'x', and I especially don't want to
>>>>> INSERT it. It would be a duplicate of 'myoldobject'.
>>>>>
>>>>> Is there a way to copy an orm object and tell it "don't ever save this I
>>>>> just want to keep it around to look at"?
>>>>>
>>>>> Alternatively I can just copy all the attributes to a dict(), but that's
>>>>> a bit messy.
>>>>
>>>> dont put it in the Session.
>>>
>>> That makes sense. But how do I not do that? As in your example code above
>>> I'm not adding it to a session, at least not intentionally.
>>
>> don't call Session.add(). the code above doesn't add to a session unless
>> you're using some special extensions like Session.mapper.
>
> As shown exactly in the code above, I do *not* call Session.add().
>
> It appears to be doing the add when it hits the ForeignKey field. Then it not
> only does an add it also attempts an INSERT (which thankfully fails since the
> object is not ready to be saved).
you mean a relationship(). Yeah, if you do this:
x = MyObject()
foo_bar = Session.query(FooBar).first()
x.some_related = foo_bar
where "some_related" has a backref to "collection_of_myobject", the cascade
will put it in to that session which FooBar belongs. This behavior is
configurable via the "cascade" argument on relationship(), and even more so
using the new "cascade_backrefs" flag available in 0.6.5. But also you need
to decide what you are really trying to do here, if you even want FooBar
populated on your non-persisted object.
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