Related polymorphic query support inc select_related and prefetch_related #545
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@pgammans Thanks, this seems to be very useful improvement. Also I thing part of this PR should be change of documentation to reflect this, e.g.: https://django-polymorphic.readthedocs.io/en/stable/advanced.html?highlight=select_related#restrictions-caveats |
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implement support for a single query for select related base fetches across polymorphic models. adds a polymorphic QuerySet Mixin to enable non polymorphic models to fetch related models. fixes: jazzband#198 jazzband#436 jazzband#359 jazzband#244 possible fixes: jazzband#498: support for prefetch_related cannot fetch attributes not on all child models or via class names related: jazzband#531
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it will be really nice to have this. there seems to be some minor formatting issues in the latest commits. @pgammans would it be possible to fix them? |
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Are you going to merge it one day? |
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This pull request add support for select related and general related queries.
Summary
To take advantage of this it requires that the plain Django model either adds a custom query set manager and uses that for queries where it wants the related object to be transmogrify into the final polymorphic type of
that the default manager's queryset uses/ has PolymorphicQuerySetMixin or PolymorphicRelatedQuerySet as a base class
ie
class PlainModel(models.Model): objects = models.Manager.from_queryset(PolymorphicRelatedQuerySet)()The default Django select_related can be used including which means this is simple to use from the Django admin.
Performance
When using select_related we archive fetch of the data in a single query including all information required to transmogrify the related object. This is an improvement from n+1 (main line) or models + 1 (with #531)
Notes
It has minimal support for prefetch_related cannot fetch attributes not on all child models or via class names this may fix #498
Fixes: #198 #436 #359 #244