Re: [sqlalchemy] turning only loaded columns into a dict

[Jonathan Vanasco]

On Wednesday, May 2, 2018 at 5:53:56 PM UTC-4, Mike Bayer wrote:
>
> if you only care about things that are loaded, like before, look in 
> inspect(instance).dict , that's what's loaded 
>

Thanks. I'll migrate my proof-of-concept to use `inspect`.


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Re: [sqlalchemy] turning only loaded columns into a dict

[Mike Bayer]

if you only care about things that are loaded, like before, look in
inspect(instance).dict , that's what's loaded


On Wed, May 2, 2018 at 4:24 PM, Jonathan Vanasco  wrote:
> I have a mixin that helps convert object to JSON using a `columns_as_dict`
> method.
>
> it looks like this:
>
> from sqlalchemy.orm import class_mapper as sa_class_mapper
>
> class Mixin(object):
> def columns_as_dict(self):
> _cls = self.__class__
> return dict((col.name, getattr(self, col.name)) for col in
> sa_class_mapper(_cls).mapped_table.c)
>
>
> I pinpointed a performance issue where the db was getting hit when
> `load_only` was used on the objects.
>
> The simplest fix I could think of, is fetching column values from the
> object's dict instead of via getattr .  Is there a more appropriate way?
>
> from sqlalchemy.orm import class_mapper as sa_class_mapper
>
> class Mixin(object):
> def columns_as_dict(self):
>  _cls = self.__class__
>  return {col.name: self.__dict__[col.name]
>  for col in sa_class_mapper(_cls).mapped_table.c
>  if col.name in self.__dict__
>  }
>
>
> --
> 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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http://www.sqlalchemy.org/

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[sqlalchemy] turning only loaded columns into a dict

[Jonathan Vanasco]

I have a mixin that helps convert object to JSON using a `columns_as_dict` 
method.

it looks like this:

from sqlalchemy.orm import class_mapper as sa_class_mapper

class Mixin(object):
def columns_as_dict(self):
_cls = self.__class__
return dict((col.name, getattr(self, col.name)) for col in 
sa_class_mapper(_cls).mapped_table.c)


I pinpointed a performance issue where the db was getting hit when 
`load_only` was used on the objects.

The simplest fix I could think of, is fetching column values from the 
object's dict instead of via getattr .  Is there a more appropriate way?

from sqlalchemy.orm import class_mapper as sa_class_mapper

class Mixin(object):
def columns_as_dict(self):
 _cls = self.__class__
 return {col.name: self.__dict__[col.name]
 for col in sa_class_mapper(_cls).mapped_table.c
 if col.name in self.__dict__
 }


-- 
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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