Re: [sqlalchemy] Load columns/relationships of transient objects

[Harshvardhan Gupta]

Thanks! 
make_transient_to_detached did the trick! 

ill add the answer to my question. 

On Friday, 2 March 2018 11:56:30 UTC-5, Mike Bayer wrote:
>
> please add an answer to your stackoverflow question as well 
>
> On Fri, Mar 2, 2018 at 11:55 AM, Mike Bayer  > wrote: 
> > On Fri, Mar 2, 2018 at 11:55 AM, Harshvardhan Gupta 
> >  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 
> >>>  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 
> >>> >>  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 
> >>> >> >>>  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. 
> >>> >> >>> > --- 
> >>> >> >>> > You received this message because you are subscribed to the 
> >>> >> >>> > Google 
> >>> >> >>> > Groups "sqlalchemy" group. 
> >>> >> >>> > To unsubscribe from this group and stop receiving emails from 
> it, 
> >>> >> >>> > send 
> >>> >> >>> > an email to sqlalchemy+...@googlegroups.com. 
> >>> >> >>> > To post to this group, send email to 
> sqlal...@googlegroups.com. 
> >>> >> >>> > Visit this group at 
> https://groups.google.com/group/sqlalchemy. 
> >>> >> >>> > For more options, visit https://groups.google.com/d/optout. 
> >>> >> > 
> >>> >> > -- 
> >>> >> > SQLAlchemy - 
> >>> >> > The Python SQL Toolkit and Object Relational Mapper 
> >>> >> > 
> >>> >> > http://www.sqlalchemy.org/ 
> 

Re: [sqlalchemy] Load columns/relationships of transient objects

[Mike Bayer]

please add an answer to your stackoverflow question as well

On Fri, Mar 2, 2018 at 11:55 AM, Mike Bayer  wrote:
> On Fri, Mar 2, 2018 at 11:55 AM, Harshvardhan Gupta
>  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
>>>  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
>>> >>  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
>>> >> >>>  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.
>>> >> >>> > ---
>>> >> >>> > You received this message because you are subscribed to the
>>> >> >>> > Google
>>> >> >>> > Groups "sqlalchemy" group.
>>> >> >>> > To unsubscribe from this group and stop receiving emails from it,
>>> >> >>> > send
>>> >> >>> > an email to sqlalchemy+...@googlegroups.com.
>>> >> >>> > To post to this group, send email to sqlal...@googlegroups.com.
>>> >> >>> > Visit this group at https://groups.google.com/group/sqlalchemy.
>>> >> >>> > For more options, visit https://groups.google.com/d/optout.
>>> >> >
>>> >> > --
>>> >> > 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.
>>> >> > ---
>>> >> > You received this message because you are subscribed to the Google
>>> >> > Groups
>>> >> > "sqlalchemy" group.
>>> >> > To unsubscribe from this group and stop receiving emails from it,
>>> >> > send
>>> >> > an
>>> >> > email to sqlalchemy+...@googlegroups.com.
>>> >> > To post to this group, send email to sqlal...@googlegroups.com.
>>> >> > Visit this group at 

Re: [sqlalchemy] Load columns/relationships of transient objects

[Mike Bayer]

On Fri, Mar 2, 2018 at 11:55 AM, Harshvardhan Gupta
 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
>>  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
>> >>  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
>> >> >>>  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.
>> >> >>> > ---
>> >> >>> > You received this message because you are subscribed to the
>> >> >>> > Google
>> >> >>> > Groups "sqlalchemy" group.
>> >> >>> > To unsubscribe from this group and stop receiving emails from it,
>> >> >>> > send
>> >> >>> > an email to sqlalchemy+...@googlegroups.com.
>> >> >>> > To post to this group, send email to sqlal...@googlegroups.com.
>> >> >>> > Visit this group at https://groups.google.com/group/sqlalchemy.
>> >> >>> > For more options, visit https://groups.google.com/d/optout.
>> >> >
>> >> > --
>> >> > 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.
>> >> > ---
>> >> > You received this message because you are subscribed to the Google
>> >> > Groups
>> >> > "sqlalchemy" group.
>> >> > To unsubscribe from this group and stop receiving emails from it,
>> >> > send
>> >> > an
>> >> > email to sqlalchemy+...@googlegroups.com.
>> >> > To post to this group, send email to sqlal...@googlegroups.com.
>> >> > Visit this group at https://groups.google.com/group/sqlalchemy.
>> >> > For more options, visit https://groups.google.com/d/optout.
>> >
>> > --
>> > SQLAlchemy -
>> > The Python SQL Toolkit and Object Relational Mapper
>> >
>> > http://www.sqlalchemy.org/
>> >
>> > To post example code, please provide an MCVE: Minimal, Complete, 

Re: [sqlalchemy] Load columns/relationships of transient objects

[Harshvardhan Gupta]

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. 

On Friday, 2 March 2018 11:51:20 UTC-5, Mike Bayer wrote:
>
> On Fri, Mar 2, 2018 at 11:30 AM, Harshvardhan Gupta 
>  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 
> >>  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 
> >> >>>  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. 
> >> >>> > --- 
> >> >>> > You received this message because you are subscribed to the 
> Google 
> >> >>> > Groups "sqlalchemy" group. 
> >> >>> > To unsubscribe from this group and stop receiving emails from it, 
> >> >>> > send 
> >> >>> > an email to sqlalchemy+...@googlegroups.com. 
> >> >>> > To post to this group, send email to sqlal...@googlegroups.com. 
> >> >>> > Visit this group at https://groups.google.com/group/sqlalchemy. 
> >> >>> > For more options, visit https://groups.google.com/d/optout. 
> >> > 
> >> > -- 
> >> > 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. 
> >> > --- 
> >> > You received this message because you are subscribed to the Google 
> >> > Groups 
> >> > "sqlalchemy" group. 
> >> > To unsubscribe from this group and stop receiving emails from it, 
> send 
> >> > an 
> >> > email to sqlalchemy+...@googlegroups.com. 
> >> > To post to this group, send email to sqlal...@googlegroups.com. 
> >> > Visit this group at https://groups.google.com/group/sqlalchemy. 
> >> > For more options, visit https://groups.google.com/d/optout. 
> > 
> > -- 
> > 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. 
> > --- 
> > You received this message because you are subscribed to the Google 
> Groups 
> > "sqlalchemy" group. 
> > To unsubscribe from this group and stop receiving emails from it, send 
> an 
> > email to sqlalchemy+...@googlegroups.com . 
> > To post to this group, send email to sqlal...@googlegroups.com 
> . 
> > 

Re: [sqlalchemy] Load columns/relationships of transient objects

[Mike Bayer]

On Fri, Mar 2, 2018 at 11:30 AM, Harshvardhan Gupta
 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
>>  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
>> >>>  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.
>> >>> > ---
>> >>> > You received this message because you are subscribed to the Google
>> >>> > Groups "sqlalchemy" group.
>> >>> > To unsubscribe from this group and stop receiving emails from it,
>> >>> > send
>> >>> > an email to sqlalchemy+...@googlegroups.com.
>> >>> > To post to this group, send email to sqlal...@googlegroups.com.
>> >>> > Visit this group at https://groups.google.com/group/sqlalchemy.
>> >>> > For more options, visit https://groups.google.com/d/optout.
>> >
>> > --
>> > 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.
>> > ---
>> > You received this message because you are subscribed to the Google
>> > Groups
>> > "sqlalchemy" group.
>> > To unsubscribe from this group and stop receiving emails from it, send
>> > an
>> > email to sqlalchemy+...@googlegroups.com.
>> > To post to this group, send email to sqlal...@googlegroups.com.
>> > Visit this group at https://groups.google.com/group/sqlalchemy.
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Re: [sqlalchemy] Load columns/relationships of transient objects

[Harshvardhan Gupta]

There is no way to achieve what I want without doing the query? 
merge seems to do the whole 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 
>  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 
> >>>  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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> send 
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> >>> > For more options, visit https://groups.google.com/d/optout. 
> > 
> > -- 
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> > 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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Re: [sqlalchemy] Load columns/relationships of transient objects

[Mike Bayer]

On Fri, Mar 2, 2018 at 11:21 AM, Harshvardhan Gupta
 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
>>>  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.
>>> > ---
>>> > You received this message because you are subscribed to the Google
>>> > Groups "sqlalchemy" group.
>>> > To unsubscribe from this group and stop receiving emails from it, send
>>> > an email to sqlalchemy+...@googlegroups.com.
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>>> > For more options, visit https://groups.google.com/d/optout.
>
> --
> 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
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Re: [sqlalchemy] Load columns/relationships of transient objects

[Harshvardhan Gupta]

I also tried loading a related attribute , and it still returns None. 

-- 
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The Python SQL Toolkit and Object Relational Mapper

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Re: [sqlalchemy] Load columns/relationships of transient objects

[Harshvardhan Gupta]

I also tried loading a related attribute , and it still returns None. 

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 
>>  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. 
>> > --- 
>> > You received this message because you are subscribed to the Google 
>> Groups "sqlalchemy" group. 
>> > To unsubscribe from this group and stop receiving emails from it, send 
>> an email to sqlalchemy+...@googlegroups.com. 
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>> > Visit this group at https://groups.google.com/group/sqlalchemy. 
>> > For more options, visit https://groups.google.com/d/optout. 
>>
>

-- 
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The Python SQL Toolkit and Object Relational Mapper

http://www.sqlalchemy.org/

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Re: [sqlalchemy] Load columns/relationships of transient objects

[Harshvardhan Gupta]

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 
>  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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> . 
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> > For more options, visit https://groups.google.com/d/optout. 
>

-- 
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http://www.sqlalchemy.org/

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Re: [sqlalchemy] Load columns/relationships of transient objects

[Mike Bayer]

On Fri, Mar 2, 2018 at 10:52 AM, Harshvardhan Gupta
 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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Re: [sqlalchemy] Load columns/relationships of transient objects

[Harshvardhan Gupta]

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. 

-- 
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The Python SQL Toolkit and Object Relational Mapper

http://www.sqlalchemy.org/

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Re: [sqlalchemy] Load columns/relationships of transient objects

[Mike Bayer]

On Fri, Mar 2, 2018 at 12:38 AM, Harshvardhan Gupta
 wrote:
> I am using flask-sqlalchemy , and flask login.
>
> Flask login requires a user object to identify the current user.
>
> So I give it something like :
>
> user = User(id=1)
>
> where User is an flask-sqlalchemy db model.
>
> Note that this does not actually perform a query to the db.
>
> Later on, I may want to access the email attribute of user, so I would do :
> user.email.
> Now I would expect a db query to be run and fetch the email from the
> database.
>
> There seems to be some discussion about this issue , but I was unable to
> find a proper solution for it.
>
> Some help will be great

the correct solution would be to please load the User object from the
database so that you avoid having to guess that User(id=1) even exists
or is a valid user.

The less correct solution tis that you can associate this
not-necessarily-existing User object with a Session to provide
relationship lazy loading using the enable_relationship_loading()
method on your object:
http://docs.sqlalchemy.org/en/latest/orm/session_api.html#sqlalchemy.orm.session.Session.enable_relationship_loading


>
> --
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>
> http://www.sqlalchemy.org/
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