Re: [sqlalchemy] mapper on a temporary class

[Kent Bower]

Excellent.  As always, thanks very much for your time and answers (let
alone awesome software)!


On Wed, Jan 27, 2021 at 1:25 PM Mike Bayer  wrote:

>
>
> On Tue, Jan 26, 2021, at 9:01 PM, Kent Bower wrote:
>
> Thanks a ton for your responses.
>
> Do all the normal columns of an aliased class need to match the ad-hoc
> select to which I map the alias?
>
>
> handwavy handwavy sort of yes, sort of no?there needs to be a 1-1
> correspondence of columns, yes, aliasedclass can't define additional
> attributes that arent there normally.  as to how they are lined up, there's
> an option to do it by name in the aliased() function adapt_on_names.
> otherwise it's expected that your select() is derived from the Table
> objects that are originally mapped.
>
>
>
> > oh if the class doesn't have a mapper, then defintiely, just make
> ad-hoc subclasses of it and map to those.vastly easier that way.
>
> Mapping to a subclass would be different from mapping directly to an
> ad-hoc class?
>
>
> if the class itself is ad-hoc, then you're fine, you can make new classes
> with mappers all you want and they are GCed if you lose them (assuming no
> relationships involving long-lived classes with backrefs), yes.
>
>
>
>
>
>
>  (Mostly I’m concerned whether the very act of adding a mapper to a class
> will keep the reference and prevent its garbage collection or in some other
> way modify the “main” mappers, especially if this is done via a thread.
> Like, would that modify the compiled mappers for the entire process...
> these are the things running through my head.)
>
>
> the configure_mappers() function these days is threadsafe, it uses a
> mutex, so you are "good" there but there's a mutex involved if you are
> looking for high levels of concurrency.   if your ad-hoc classes are not
> subclasses of any long lived classes and if you are careful to limit
> relationships to only point to long lived classes and not have any
> backrefs, it should be OK.  I'd test it though :)set up a weakref.ref()
> to your ad-hoc mapper objects and make sure those ref objects get their
> callback hook invoked.
>
>
>
>
>
>
> On Tue, Jan 26, 2021 at 8:18 PM Mike Bayer 
> wrote:
>
>
>
>
> On Tue, Jan 26, 2021, at 7:31 PM, Kent Bower wrote:
>
> I should have given these details from the get-go:  the use case is a
> specialized select() (dynamically built) which would be extremely
> convenient to map relationships against for convenience in subquery
> loading, etc. So, the class would not already have a mapper.  Can I pass
> non_primary=True anyway, or won’t this work?
>
>
> oh if the class doesn't have a mapper, then defintiely, just make ad-hoc
> subclasses of it and map to those.vastly easier that way.
>
>
>
>
>
>
> On Tue, Jan 26, 2021 at 6:18 PM Mike Bayer 
> wrote:
>
>
>
>
> On Tue, Jan 26, 2021, at 3:16 PM, Kent wrote:
>
> Question: if I add a mapper to a class that is only needed temporarily,
> does using the mapper compile it along side my "normal" mappers such that
> I'll leak memory when I mean for the class to be garbage collected?
>
> Put another way, can I add a mapper to a class that doesn't influence my
> "main mappers" and gets thrown away when the class is thrown away or is
> that not possible?
>
>
> Assuming the class already has a mapper, and this is an additional mapper
> that maps the class in a different way, this feature is called a
> "non-primary mapper" and requires that you pass the non_primary=True flag.
>   If you are using non-primary mappers, then yes they get garbage collected.
>
> This is also a deprecated feature that won't be in SQLAlchemy 2.0.The
> only use case we can identify for "non-primary mappers" is when you want to
> create a relationship() to one, and for that use case we now support the
> "Relationship to AliasedClass" pattern.
>
> For anything else involving retrieving a class from an alternate
> selectable of some kind, you should be able to use AliasedClass for, e.g.
> sqlalchemy.orm.aliased(), so I would recommend using that instead unless
> you are on a very old version of SQLAlchemy.
>
>
>
>
>
>
>
>
> Thanks in advance,
> Kent
>
>
> --
> 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+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/sqlalchemy/df03ce24-3986-450c-8c3a-a020d5d6adccn%40googlegroups.com
> 
> .
>
>
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper

Re: [sqlalchemy] mapper on a temporary class

[Mike Bayer]

On Tue, Jan 26, 2021, at 9:01 PM, Kent Bower wrote:
> Thanks a ton for your responses. 
> 
> Do all the normal columns of an aliased class need to match the ad-hoc select 
> to which I map the alias?

handwavy handwavy sort of yes, sort of no?there needs to be a 1-1 
correspondence of columns, yes, aliasedclass can't define additional attributes 
that arent there normally.  as to how they are lined up, there's an option to 
do it by name in the aliased() function adapt_on_names.  otherwise it's 
expected that your select() is derived from the Table objects that are 
originally mapped.


> 
> > oh if the class doesn't have a mapper, then defintiely, just make ad-hoc 
> > subclasses of it and map to those.vastly easier that way.
> 
> Mapping to a subclass would be different from mapping directly to an ad-hoc 
> class? 

if the class itself is ad-hoc, then you're fine, you can make new classes with 
mappers all you want and they are GCed if you lose them (assuming no 
relationships involving long-lived classes with backrefs), yes.




> 
> 
>  (Mostly I’m concerned whether the very act of adding a mapper to a class 
> will keep the reference and prevent its garbage collection or in some other 
> way modify the “main” mappers, especially if this is done via a thread. Like, 
> would that modify the compiled mappers for the entire process... these are 
> the things running through my head.)

the configure_mappers() function these days is threadsafe, it uses a mutex, so 
you are "good" there but there's a mutex involved if you are looking for high 
levels of concurrency.   if your ad-hoc classes are not subclasses of any long 
lived classes and if you are careful to limit relationships to only point to 
long lived classes and not have any backrefs, it should be OK.  I'd test it 
though :)set up a weakref.ref() to your ad-hoc mapper objects and make sure 
those ref objects get their callback hook invoked.




> 
> 
> On Tue, Jan 26, 2021 at 8:18 PM Mike Bayer  wrote:
>> __
>> 
>> 
>> On Tue, Jan 26, 2021, at 7:31 PM, Kent Bower wrote:
>>> I should have given these details from the get-go:  the use case is a 
>>> specialized select() (dynamically built) which would be extremely 
>>> convenient to map relationships against for convenience in subquery 
>>> loading, etc. So, the class would not already have a mapper.  Can I pass 
>>> non_primary=True anyway, or won’t this work?
>> 
>> oh if the class doesn't have a mapper, then defintiely, just make ad-hoc 
>> subclasses of it and map to those.vastly easier that way.
>> 
>> 
>> 
>>> 
>>> 
>>> 
>>> On Tue, Jan 26, 2021 at 6:18 PM Mike Bayer  wrote:
 __
 
 
 On Tue, Jan 26, 2021, at 3:16 PM, Kent wrote:
> Question: if I add a mapper to a class that is only needed temporarily, 
> does using the mapper compile it along side my "normal" mappers such that 
> I'll leak memory when I mean for the class to be garbage collected?
> 
> Put another way, can I add a mapper to a class that doesn't influence my 
> "main mappers" and gets thrown away when the class is thrown away or is 
> that not possible?
 
 Assuming the class already has a mapper, and this is an additional mapper 
 that maps the class in a different way, this feature is called a 
 "non-primary mapper" and requires that you pass the non_primary=True flag. 
If you are using non-primary mappers, then yes they get garbage 
 collected.
 
 This is also a deprecated feature that won't be in SQLAlchemy 2.0.The 
 only use case we can identify for "non-primary mappers" is when you want 
 to create a relationship() to one, and for that use case we now support 
 the "Relationship to AliasedClass" pattern.
 
 For anything else involving retrieving a class from an alternate 
 selectable of some kind, you should be able to use AliasedClass for, e.g. 
 sqlalchemy.orm.aliased(), so I would recommend using that instead unless 
 you are on a very old version of SQLAlchemy.
 
 
 
 
 
 
 
 
> Thanks in advance,
> Kent
> 

> -- 
> 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+unsubscr...@googlegroups.com.
> To view this discussion on the web visit 
> https://groups.google.com/d/msgid/sqlalchemy/df03ce24-3986-450c-8c3a-a020d5d6adccn%40googlegroups.com
>  
> 

Re: [sqlalchemy] mapper on a temporary class

[Kent Bower]

Thanks a ton for your responses.

Do all the normal columns of an aliased class need to match the ad-hoc
select to which I map the alias?

> oh if the class doesn't have a mapper, then defintiely, just make ad-hoc
subclasses of it and map to those.vastly easier that way.

Mapping to a subclass would be different from mapping directly to an ad-hoc
class?  (Mostly I’m concerned whether the very act of adding a mapper to a
class will keep the reference and prevent its garbage collection or in some
other way modify the “main” mappers, especially if this is done via a
thread. Like, would that modify the compiled mappers for the entire
process... these are the things running through my head.)


On Tue, Jan 26, 2021 at 8:18 PM Mike Bayer  wrote:

>
>
> On Tue, Jan 26, 2021, at 7:31 PM, Kent Bower wrote:
>
> I should have given these details from the get-go:  the use case is a
> specialized select() (dynamically built) which would be extremely
> convenient to map relationships against for convenience in subquery
> loading, etc. So, the class would not already have a mapper.  Can I pass
> non_primary=True anyway, or won’t this work?
>
>
> oh if the class doesn't have a mapper, then defintiely, just make ad-hoc
> subclasses of it and map to those.vastly easier that way.
>
>
>
>
>
> On Tue, Jan 26, 2021 at 6:18 PM Mike Bayer 
> wrote:
>
>
>
>
> On Tue, Jan 26, 2021, at 3:16 PM, Kent wrote:
>
> Question: if I add a mapper to a class that is only needed temporarily,
> does using the mapper compile it along side my "normal" mappers such that
> I'll leak memory when I mean for the class to be garbage collected?
>
> Put another way, can I add a mapper to a class that doesn't influence my
> "main mappers" and gets thrown away when the class is thrown away or is
> that not possible?
>
>
> Assuming the class already has a mapper, and this is an additional mapper
> that maps the class in a different way, this feature is called a
> "non-primary mapper" and requires that you pass the non_primary=True flag.
>   If you are using non-primary mappers, then yes they get garbage collected.
>
> This is also a deprecated feature that won't be in SQLAlchemy 2.0.The
> only use case we can identify for "non-primary mappers" is when you want to
> create a relationship() to one, and for that use case we now support the
> "Relationship to AliasedClass" pattern.
>
> For anything else involving retrieving a class from an alternate
> selectable of some kind, you should be able to use AliasedClass for, e.g.
> sqlalchemy.orm.aliased(), so I would recommend using that instead unless
> you are on a very old version of SQLAlchemy.
>
>
>
>
>
>
>
>
> Thanks in advance,
> Kent
>
>
> --
> 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+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/sqlalchemy/df03ce24-3986-450c-8c3a-a020d5d6adccn%40googlegroups.com
> 
> .
>
>
>
> --
> 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 a topic in the
> Google Groups "sqlalchemy" group.
> To unsubscribe from this topic, visit
> https://groups.google.com/d/topic/sqlalchemy/IAqOQFpiB20/unsubscribe.
> To unsubscribe from this group and all its topics, send an email to
> sqlalchemy+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/sqlalchemy/c8f7f84e-af90-450c-9289-ed84fc6996a9%40www.fastmail.com
> 
> .
>
>
> --
> 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+unsubscr...@googlegroups.com.
>
> To view this discussion on the web visit
> 

Re: [sqlalchemy] mapper on a temporary class

[Mike Bayer]

On Tue, Jan 26, 2021, at 7:31 PM, Kent Bower wrote:
> I should have given these details from the get-go:  the use case is a 
> specialized select() (dynamically built) which would be extremely convenient 
> to map relationships against for convenience in subquery loading, etc. So, 
> the class would not already have a mapper.  Can I pass non_primary=True 
> anyway, or won’t this work?

oh if the class doesn't have a mapper, then defintiely, just make ad-hoc 
subclasses of it and map to those.vastly easier that way.



> 
> 
> On Tue, Jan 26, 2021 at 6:18 PM Mike Bayer  wrote:
>> __
>> 
>> 
>> On Tue, Jan 26, 2021, at 3:16 PM, Kent wrote:
>>> Question: if I add a mapper to a class that is only needed temporarily, 
>>> does using the mapper compile it along side my "normal" mappers such that 
>>> I'll leak memory when I mean for the class to be garbage collected?
>>> 
>>> Put another way, can I add a mapper to a class that doesn't influence my 
>>> "main mappers" and gets thrown away when the class is thrown away or is 
>>> that not possible?
>> 
>> Assuming the class already has a mapper, and this is an additional mapper 
>> that maps the class in a different way, this feature is called a 
>> "non-primary mapper" and requires that you pass the non_primary=True flag.   
>>  If you are using non-primary mappers, then yes they get garbage collected.
>> 
>> This is also a deprecated feature that won't be in SQLAlchemy 2.0.The 
>> only use case we can identify for "non-primary mappers" is when you want to 
>> create a relationship() to one, and for that use case we now support the 
>> "Relationship to AliasedClass" pattern.
>> 
>> For anything else involving retrieving a class from an alternate selectable 
>> of some kind, you should be able to use AliasedClass for, e.g. 
>> sqlalchemy.orm.aliased(), so I would recommend using that instead unless you 
>> are on a very old version of SQLAlchemy.
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>>> Thanks in advance,
>>> Kent
>>> 

>>> -- 
>>> 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+unsubscr...@googlegroups.com.
>>> To view this discussion on the web visit 
>>> https://groups.google.com/d/msgid/sqlalchemy/df03ce24-3986-450c-8c3a-a020d5d6adccn%40googlegroups.com
>>>  
>>> .
>> 
>> 

>> -- 
>> 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 a topic in the 
>> Google Groups "sqlalchemy" group.
>> To unsubscribe from this topic, visit 
>> https://groups.google.com/d/topic/sqlalchemy/IAqOQFpiB20/unsubscribe.
>> To unsubscribe from this group and all its topics, send an email to 
>> sqlalchemy+unsubscr...@googlegroups.com.
>> To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/sqlalchemy/c8f7f84e-af90-450c-9289-ed84fc6996a9%40www.fastmail.com
>>  
>> .
> 

> -- 
> 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+unsubscr...@googlegroups.com.
> To view this discussion on the web visit 
> https://groups.google.com/d/msgid/sqlalchemy/CANnF6aEAcuCRJrAQDWYrDGVmv5k7OuXNC_AXgrqDO00L3j%3D%2BAg%40mail.gmail.com
>  
> .

-- 
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 

Re: [sqlalchemy] mapper on a temporary class

[Mike Bayer]

On Tue, Jan 26, 2021, at 7:31 PM, Kent Bower wrote:
> I should have given these details from the get-go:  the use case is a 
> specialized select() (dynamically built) which would be extremely convenient 
> to map relationships against for convenience in subquery loading, etc. So, 
> the class would not already have a mapper.  Can I pass non_primary=True 
> anyway, or won’t this work?

You can use relationship loading with the aliased class approach too; the 
relationships that are on the class would just work against your altered 
select() statement.  Also I would recommend ditching subqueryloading in favor 
of selectinload() , which is better than subqueryload in pretty much every way.

if you want to make totally custom relatoinships to new classes that aren't on 
the class normally, and such and have different primaryjoin conditions and all 
that, and it's not possible to have these relationships at least as 
placeholders on the normal class, then it starts to look like you want to make 
a subclass and map to that with concrete=True.


> 
> 
> On Tue, Jan 26, 2021 at 6:18 PM Mike Bayer  wrote:
>> __
>> 
>> 
>> On Tue, Jan 26, 2021, at 3:16 PM, Kent wrote:
>>> Question: if I add a mapper to a class that is only needed temporarily, 
>>> does using the mapper compile it along side my "normal" mappers such that 
>>> I'll leak memory when I mean for the class to be garbage collected?
>>> 
>>> Put another way, can I add a mapper to a class that doesn't influence my 
>>> "main mappers" and gets thrown away when the class is thrown away or is 
>>> that not possible?
>> 
>> Assuming the class already has a mapper, and this is an additional mapper 
>> that maps the class in a different way, this feature is called a 
>> "non-primary mapper" and requires that you pass the non_primary=True flag.   
>>  If you are using non-primary mappers, then yes they get garbage collected.
>> 
>> This is also a deprecated feature that won't be in SQLAlchemy 2.0.The 
>> only use case we can identify for "non-primary mappers" is when you want to 
>> create a relationship() to one, and for that use case we now support the 
>> "Relationship to AliasedClass" pattern.
>> 
>> For anything else involving retrieving a class from an alternate selectable 
>> of some kind, you should be able to use AliasedClass for, e.g. 
>> sqlalchemy.orm.aliased(), so I would recommend using that instead unless you 
>> are on a very old version of SQLAlchemy.
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>>> Thanks in advance,
>>> Kent
>>> 

>>> -- 
>>> 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+unsubscr...@googlegroups.com.
>>> To view this discussion on the web visit 
>>> https://groups.google.com/d/msgid/sqlalchemy/df03ce24-3986-450c-8c3a-a020d5d6adccn%40googlegroups.com
>>>  
>>> .
>> 
>> 

>> -- 
>> 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 a topic in the 
>> Google Groups "sqlalchemy" group.
>> To unsubscribe from this topic, visit 
>> https://groups.google.com/d/topic/sqlalchemy/IAqOQFpiB20/unsubscribe.
>> To unsubscribe from this group and all its topics, send an email to 
>> sqlalchemy+unsubscr...@googlegroups.com.
>> To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/sqlalchemy/c8f7f84e-af90-450c-9289-ed84fc6996a9%40www.fastmail.com
>>  
>> .
> 

> -- 
> 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+unsubscr...@googlegroups.com.
> To view this discussion on the web visit 
> https://groups.google.com/d/msgid/sqlalchemy/CANnF6aEAcuCRJrAQDWYrDGVmv5k7OuXNC_AXgrqDO00L3j%3D%2BAg%40mail.gmail.com
>  
> 

Re: [sqlalchemy] mapper on a temporary class

[Kent Bower]

I should have given these details from the get-go:  the use case is a
specialized select() (dynamically built) which would be extremely
convenient to map relationships against for convenience in subquery
loading, etc. So, the class would not already have a mapper.  Can I pass
non_primary=True anyway, or won’t this work?


On Tue, Jan 26, 2021 at 6:18 PM Mike Bayer  wrote:

>
>
> On Tue, Jan 26, 2021, at 3:16 PM, Kent wrote:
>
> Question: if I add a mapper to a class that is only needed temporarily,
> does using the mapper compile it along side my "normal" mappers such that
> I'll leak memory when I mean for the class to be garbage collected?
>
> Put another way, can I add a mapper to a class that doesn't influence my
> "main mappers" and gets thrown away when the class is thrown away or is
> that not possible?
>
>
> Assuming the class already has a mapper, and this is an additional mapper
> that maps the class in a different way, this feature is called a
> "non-primary mapper" and requires that you pass the non_primary=True flag.
>   If you are using non-primary mappers, then yes they get garbage collected.
>
> This is also a deprecated feature that won't be in SQLAlchemy 2.0.The
> only use case we can identify for "non-primary mappers" is when you want to
> create a relationship() to one, and for that use case we now support the
> "Relationship to AliasedClass" pattern.
>
> For anything else involving retrieving a class from an alternate
> selectable of some kind, you should be able to use AliasedClass for, e.g.
> sqlalchemy.orm.aliased(), so I would recommend using that instead unless
> you are on a very old version of SQLAlchemy.
>
>
>
>
>
>
>
>
> Thanks in advance,
> Kent
>
>
> --
> 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+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/sqlalchemy/df03ce24-3986-450c-8c3a-a020d5d6adccn%40googlegroups.com
> 
> .
>
>
> --
> 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 a topic in the
> Google Groups "sqlalchemy" group.
> To unsubscribe from this topic, visit
> https://groups.google.com/d/topic/sqlalchemy/IAqOQFpiB20/unsubscribe.
> To unsubscribe from this group and all its topics, send an email to
> sqlalchemy+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/sqlalchemy/c8f7f84e-af90-450c-9289-ed84fc6996a9%40www.fastmail.com
> 
> .
>

-- 
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+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/sqlalchemy/CANnF6aEAcuCRJrAQDWYrDGVmv5k7OuXNC_AXgrqDO00L3j%3D%2BAg%40mail.gmail.com.

Re: [sqlalchemy] mapper on a temporary class

[Mike Bayer]

On Tue, Jan 26, 2021, at 3:16 PM, Kent wrote:
> Question: if I add a mapper to a class that is only needed temporarily, does 
> using the mapper compile it along side my "normal" mappers such that I'll 
> leak memory when I mean for the class to be garbage collected?
> 
> Put another way, can I add a mapper to a class that doesn't influence my 
> "main mappers" and gets thrown away when the class is thrown away or is that 
> not possible?

Assuming the class already has a mapper, and this is an additional mapper that 
maps the class in a different way, this feature is called a "non-primary 
mapper" and requires that you pass the non_primary=True flag.If you are 
using non-primary mappers, then yes they get garbage collected.

This is also a deprecated feature that won't be in SQLAlchemy 2.0.The only 
use case we can identify for "non-primary mappers" is when you want to create a 
relationship() to one, and for that use case we now support the "Relationship 
to AliasedClass" pattern.

For anything else involving retrieving a class from an alternate selectable of 
some kind, you should be able to use AliasedClass for, e.g. 
sqlalchemy.orm.aliased(), so I would recommend using that instead unless you 
are on a very old version of SQLAlchemy.








> Thanks in advance,
> Kent
> 

> -- 
> 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+unsubscr...@googlegroups.com.
> To view this discussion on the web visit 
> https://groups.google.com/d/msgid/sqlalchemy/df03ce24-3986-450c-8c3a-a020d5d6adccn%40googlegroups.com
>  
> .

-- 
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+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/sqlalchemy/c8f7f84e-af90-450c-9289-ed84fc6996a9%40www.fastmail.com.

[sqlalchemy] mapper on a temporary class

[Kent]

Question: if I add a mapper to a class that is only needed temporarily, 
does using the mapper compile it along side my "normal" mappers such that 
I'll leak memory when I mean for the class to be garbage collected?

Put another way, can I add a mapper to a class that doesn't influence my 
"main mappers" and gets thrown away when the class is thrown away or is 
that not possible?

Thanks in advance,
Kent

-- 
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+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/sqlalchemy/df03ce24-3986-450c-8c3a-a020d5d6adccn%40googlegroups.com.