Parent object from collection class

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Asif Mahmud

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Jul 26, 2017, 1:18:45 PM7/26/17
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Hi, 
Is there a way to get/retrieve the parent object from a collection class's append/add method ?

Mike Bayer

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Jul 26, 2017, 3:32:45 PM7/26/17
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On Jul 26, 2017 1:18 PM, "Asif Mahmud" <ams....@gmail.com> wrote:
Hi, 
Is there a way to get/retrieve the parent object from a collection class's append/add method ?

From the method, call im_self to get the collection object itself, then use collection_adapter ( http://docs.sqlalchemy.org/en/latest/orm/collections.html?highlight=collection_adapter#sqlalchemy.orm.collections.collection_adapter ) to get the CollectionAdapter, then call adapter.owner_state.obj().


I'd recommend passing the parent object around in the first place, however as the above is esoteric and also runs the chance of failing if the parent object has been garbage collected. 

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Asif Mahmud

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Jul 26, 2017, 5:16:00 PM7/26/17
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I walked through the dir of self and found this statement is the parent object - self._sa_adapter.owner_state.object . Is it safe to use this object for making more queries inside append method?

Best wishes -
Asif Mahmud Shimon


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Mike Bayer

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Jul 26, 2017, 5:16:54 PM7/26/17
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On Wed, Jul 26, 2017 at 5:15 PM, Asif Mahmud <ams....@gmail.com> wrote:
> I walked through the dir of self and found this statement is the parent
> object - self._sa_adapter.owner_state.object . Is it safe to use this object
> for making more queries inside append method?

no, because _sa_adapter is private. The collection_adapter() function
should be used to access this attribute.
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Asif Mahmud

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Jul 26, 2017, 5:22:51 PM7/26/17
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So, doing it like this - parent = collections.collection_adapter(self).owner_state.obj() where self is the collection object. is it correct?

Best wishes -
Asif Mahmud Shimon



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Mike Bayer

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Jul 26, 2017, 5:37:14 PM7/26/17
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On Wed, Jul 26, 2017 at 5:22 PM, Asif Mahmud <ams....@gmail.com> wrote:
> So, doing it like this - parent =
> collections.collection_adapter(self).owner_state.obj() where self is the
> collection object. is it correct?

here's how you test that:

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(ForeignKey('a.id'))


from sqlalchemy.orm import collections
a1 = A(bs=[B(), B(), B()])

self = a1.bs

parent = collections.collection_adapter(self).owner_state.obj()

assert parent is a1
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Asif Mahmud

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Jul 26, 2017, 6:38:47 PM7/26/17
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Thank you so much to take the time for helping me out.

Best wishes -
Asif Mahmud Shimon



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>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
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http://www.sqlalchemy.org/

To post example code, please provide an MCVE: Minimal, Complete, and Verifiable Example.  See  http://stackoverflow.com/help/mcve for a full description.
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