One-level select_related

[OskarPersson]

This is an attempt at adding support for select_related and thus closing #198. So far it has no unit tests or documentation and has mostly been tested with Graphene-Django which is where I found my need for this.

(Getting graphene-django-optimizer to work with this is the next step!)

With my limited testing it seems to work at the first level (e.g. Parent.objects.select_related('childa__related')) but not any deeper than that (e.g. Parent.objects.select_related('childa__related__childb'))

This PR is not in a mergeable state and instead is currently mostly created for bringing the discussion further for implementing select_related with a more complete solution.

[ADR-007]

You can try something like that:

from typing import List

from polymorphic.models import PolymorphicModel
from polymorphic.query import PolymorphicQuerySet


class SelectRelatedPolymorphicQuerySet(PolymorphicQuerySet):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.used_select_related_cache = False

    def use_select_related(self):
        qs = self._clone()
        qs.used_select_related_cache = True

        return qs

    def _clone(self, *args, **kwargs):
        qs = super()._clone(*args, **kwargs)
        qs.used_select_related_cache = self.used_select_related_cache

        return qs

    def _get_real_instances(self, base_result_objects: List[PolymorphicModel]):
        if self.used_select_related_cache:
            return [item.get_real_instance() for item in base_result_objects]

        return super()._get_real_instances(base_result_objects)

from polymorphic.managers import PolymorphicManager
from polymorphic.models import PolymorphicModel

from vas.utils.models.polymorhic.querysets import SelectRelatedPolymorphicQuerySet


class SelectRelatedPolymorphicModel(PolymorphicModel):
    class Meta:
        abstract = True

    objects = PolymorphicManager.from_queryset(SelectRelatedPolymorphicQuerySet)()

    def get_real_instance(self):
        real_model = self.get_real_instance_class()

        if real_model == self.__class__:
            return self

        # allow to use cache:
        # return getattr(self, real_model.__name__.lower())
        return self._state.fields_cache[real_model.__name__.lower()]  # todo

[codecov]

Codecov Report

❌ Patch coverage is 10.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.21%. Comparing base (9399f7d) to head (f02f609).
⚠️ Report is 24 commits behind head on master.

Files with missing lines	Patch %	Lines
src/polymorphic/query.py	10.00%	8 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #395      +/-   ##
==========================================
- Coverage   74.71%   74.21%   -0.50%     
==========================================
  Files          21       21              
  Lines        1337     1346       +9     
  Branches      211      214       +3     
==========================================
  Hits          999      999              
- Misses        261      269       +8     
- Partials       77       78       +1     

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[bckohan]

Thanks for this start @OskarPersson!

I am the new leader of this project. It will take me a bit to work through the backlog of issues but this feature is also a desire of mine so I plan to revisit this as time allows. If you want to take another look that would be great too!

[bckohan]

I am closing this PR in favor of either #545 or #531

[Copilot]

Pull request overview

This PR attempts to add select_related() support for polymorphic models, addressing issue #198. The implementation modifies the _get_real_instances() method to copy select_related configuration from the base queryset to the real object querysets for each concrete polymorphic subclass.

Key changes:

• Adds logic to handle select_related configuration when fetching real instances of polymorphic models
• Filters select_related to exclude sibling model paths and isolate child-specific relations
• Preserves select_related=False behavior

---

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[Copilot]

__subclasses__() only returns direct subclasses, not all descendants in the inheritance hierarchy. For a model hierarchy like Model2A -> Model2B -> Model2C -> Model2D, calling __subclasses__() on Model2A only returns [Model2B], missing Model2C and Model2D. This could cause issues when concrete_model_name is a deeper descendant not in sub_model_names, leading to a KeyError on remove(). Consider using a recursive helper to collect all descendants, similar to the pattern in query_translate.py:_get_mro_content_type_ids().

[Copilot]

Unnecessary list comprehension brackets. Use a set comprehension or generator expression directly: sub_model_names = {m._meta.model_name for m in self.model.__subclasses__()}

Suggested change

	sub_model_names = set([m._meta.model_name for m in self.model.__subclasses__()])
	sub_model_names = {m._meta.model_name for m in self.model.__subclasses__()}

[Copilot]

The new select_related handling logic lacks test coverage. The test suite in test_orm.py has comprehensive tests for other queryset operations (defer, prefetch_related, annotate, etc.) but no tests for select_related. Consider adding tests that cover: 1) basic select_related on polymorphic models, 2) select_related with nested relations through child models, 3) select_related with multiple inheritance levels, and 4) edge cases like empty select_related or select_related(None).

[Copilot]

The code assumes self.query.select_related is a dict when it's not False, but Django's select_related can also be True (when called with no arguments like .select_related()), or an empty dict {}. Attempting operations like .pop(), in, or [] access on True will raise TypeError or AttributeError. Add a check: elif self.query.select_related is True: or elif not isinstance(self.query.select_related, dict): to handle these cases.

[Copilot]

Mutating self.query.select_related directly with pop() modifies the original queryset's configuration. Since this code is inside a loop over idlist_per_model.items(), the first iteration will remove entries from the dict, affecting subsequent iterations for other concrete classes. This should operate on a copy instead: select_related_copy = self.query.select_related.copy()

Suggested change

	for sub_name in sub_model_names:
	self.query.select_related.pop(sub_name, None)
	if concrete_model_name in self.query.select_related:
	real_objects.query.select_related = self.query.select_related[
	concrete_model_name
	]
	else:
	real_objects.query.select_related = self.query.select_related
	# Make a shallow copy to avoid mutating the original select_related dict
	select_related_copy = self.query.select_related.copy()
	for sub_name in sub_model_names:
	select_related_copy.pop(sub_name, None)
	if concrete_model_name in select_related_copy:
	real_objects.query.select_related = select_related_copy[
	concrete_model_name
	]
	else:
	real_objects.query.select_related = select_related_copy