On Mon, Oct 12, 2020 at 6:59 PM Imran Akbar <[email protected]> wrote:
>
> Hi,
>
> I'm using SQLAlchemy and am generating classes dynamically for my database
> via the Automapping functionality.
>
> I need to add a Mixin class with various helper methods to each of these
> automapped classes.
>
> I tried to create subclasses of the automapped class with the mixin class:
>
> db = create_engine(connection_string)
> automapper = automap_base()
> automapper.prepare(db, reflect=True)
> for class_variable in automapper.__subclasses__():
> new_class = type(class_variable.__name__, (class_variable, Mixins), {})
>
> but when I try to use these classes I get errors like:
>
> class _ is a subclass of AutomapBase. Mappings are not produced until the
> .prepare() method is called on the class hierarchy.
>
If you want to add your methods to *every* automapped class, you can
change the base class used by automap_base(). Something like this:
class MySpecialBaseClass(object):
# define your helper methods here
pass
automapper = automap_base(cls=MySpecialBaseClass)
This works because automap_base passes most of its arguments on to
declarative_base:
https://docs.sqlalchemy.org/en/13/orm/extensions/automap.html#sqlalchemy.ext.automap.automap_base
...and declarative_base accepts a "cls" argument which is used as the
base class:
https://docs.sqlalchemy.org/en/13/orm/extensions/declarative/api.html#sqlalchemy.ext.declarative.declarative_base
Hope that helps,
Simon
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