On Fri, Mar 2, 2018 at 11:55 AM, Harshvardhan Gupta
<harshsay...@gmail.com> wrote:
> I meant, do the query only when email is required, and not unless anything
> else is required.
> if I call merge(), the query is instantly emitted. I want it to be emitted
> only if an unloaded attribute is requested.

make the object act like detached and expired, then associate with the session:

from sqlalchemy.orm.session import make_transient_to_detached
a1 = A(id=1)
make_transient_to_detached(a1)
s.add(a1)

print("-------------------")
assert a1.data == "some data"
assert len(a1.bs) == 3





>
> On Friday, 2 March 2018 11:51:20 UTC-5, Mike Bayer wrote:
>>
>> On Fri, Mar 2, 2018 at 11:30 AM, Harshvardhan Gupta
>> <harsh...@gmail.com> wrote:
>> > There is no way to achieve what I want without doing the query?
>> > merge seems to do the whole query.
>>
>> you have a User row, and you want to load columns in that row, like
>> "full_name".    How would you like to achieve that without emitting a
>> query?
>>
>>
>>
>> > I also have asked this question on stack overflow which talks about my
>> > use
>> > case :
>> >
>> >
>> > https://stackoverflow.com/questions/49062520/querying-properties-of-transient-models-in-sqlalchemy
>> >
>> >
>> > On Friday, 2 March 2018 11:27:31 UTC-5, Mike Bayer wrote:
>> >>
>> >> On Fri, Mar 2, 2018 at 11:21 AM, Harshvardhan Gupta
>> >> <harsh...@gmail.com> wrote:
>> >> > I also tried loading a related attribute , and it still returns None.
>> >>
>> >>
>> >> you need to merge the object:
>> >>
>> >> my_user = session.merge(my_user)
>> >>
>> >> that is your only option.  E.g. do the query.
>> >>
>> >> >
>> >> >
>> >> > On Friday, 2 March 2018 11:00:47 UTC-5, Harshvardhan Gupta wrote:
>> >> >>
>> >> >> Thanks, I am able to call my object, but the attribute prints none:
>> >> >>
>> >> >>
>> >> >> E.g. my model is:
>> >> >>
>> >> >> class User(Dictifiable, db.Model, UserMixin):
>> >> >>     __tablename__ = 'user'
>> >> >>
>> >> >>     id = Column(Integer, Sequence('user_id_seq'), primary_key=True)
>> >> >>     full_name = Column(String(50))
>> >> >>
>> >> >>
>> >> >> And this is what I have done :
>> >> >>
>> >> >> `u_lazy = User(id=1)`
>> >> >> `db.session().enable_relationship_loading(u_lazy)`
>> >> >> when i try to print u_lazy.full_name, it shows null (it is non null
>> >> >> in
>> >> >> db
>> >> >> )
>> >> >>
>> >> >>
>> >> >> On Friday, 2 March 2018 10:55:11 UTC-5, Mike Bayer wrote:
>> >> >>>
>> >> >>> On Fri, Mar 2, 2018 at 10:52 AM, Harshvardhan Gupta
>> >> >>> <harsh...@gmail.com> wrote:
>> >> >>> > Thanks for the reply.
>> >> >>> >
>> >> >>> > There is a guarantee that the user will exist ,why is why I want
>> >> >>> > to
>> >> >>> > prevent that extra db query.
>> >> >>> >
>> >> >>> > When I try to do enable relationship loading ,I get the error :
>> >> >>> > Scoped session has no attribute enable relationship loading.
>> >> >>>
>> >> >>> that's a scoped_session(), not a Session, access the Session by
>> >> >>> calling it:  scoped_session().enable_relationship_loading(obj)
>> >> >>>
>> >> >>> >
>> >> >>> > --
>> >> >>> > SQLAlchemy -
>> >> >>> > The Python SQL Toolkit and Object Relational Mapper
>> >> >>> >
>> >> >>> > 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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>> >> > --
>> >> > SQLAlchemy -
>> >> > The Python SQL Toolkit and Object Relational Mapper
>> >> >
>> >> > http://www.sqlalchemy.org/
>> >> >
>> >> > To post example code, please provide an MCVE: Minimal, Complete, and
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>> > --
>> > SQLAlchemy -
>> > The Python SQL Toolkit and Object Relational Mapper
>> >
>> > http://www.sqlalchemy.org/
>> >
>> > To post example code, please provide an MCVE: Minimal, Complete, and
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>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> 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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-- 
SQLAlchemy - 
The Python SQL Toolkit and Object Relational Mapper

http://www.sqlalchemy.org/

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