Add type annotations for primary key types by model [FC-0117] by bradenmacdonald · Pull Request #534 · openedx/openedx-core

bradenmacdonald · 2026-04-07T18:29:18Z

This PR has some experimental implementations of #436 as well as moving closer toward the consistent terms preferred in OEP-68.

Second Approach: fully-typed `.id`, avoid `.pk`

(Revised from my initial attempt)

PublishableEntity, LearningPackage, Container, and Component all get a fully-typed .id field.
- PublishableEntity.id is of type PublishableEntity.PK which is a sub-type of int.
- Container.id is of type Container.PK which is a sub-type of PublishableEntity.PK.
- Component.id is of type Component.PK which is a sub-type of PublishableEntity.PK.
- LearningPackage.id is of type LearningPackage.PK which is a sub-type of int.
- Thanks to django-stubs, these types generally get propagated and used correctly pretty much everywhere.
- Example:
Likewise, CatalogCourse and CourseRun get typed.
Unfortunately, it is impossible to change the type of .pk on models that inherit PublishableEntityMixin (or any other models that use a OneToOneField as their primary_key, at least without modifying django-stubs or implementing a mypy plugin. It will always have type Any, circumventing all type definitions. However, although we cannot override its type, we can mark it as deprecated. As a result, and for consistency, accessing .pk on any of these will raise a deprecation warning in pytest/console and show a warning in your IDE:
I did not (yet?) add a deprecation warning for CatalogCourse.pk and CourseRun.pk, because (a) they are typed correctly, and (b) mypy crashes when I do 😬.

Prior Approach: fully-typed `.pk`, avoid `.id`

Expand for pros/cons/details of this earlier approach

In this earlier approach:

PublishableEntity's primary key is the .pk field, and it has type PublishableEntity.PK which is a sub-type of int.
- Example:
- In the approach I took, accessing some_entity.id will show a deprecation warning, telling you to use pk instead. And since this is an actual field called pk, any DB lookups need to be changed from e.g. entity__id=... to entity__pk=...
- A slightly less disruptive approach would be to keep the ID field called id and make an alias called entity_pk, then use deprecation warnings to encourage the use of entity_pk over id and pk; this would be more consistent with what I did for containers and components, but it's slightly annoying to type entity_pk instead of pk everywhere.
- Keeping the ID field called id and making pk a fully-typed alias is unfortunately not possible, as django-stubs forcibly overrides the type of pk unless you have a concrete field named pk as I did here.
Container and Component get Container.PK and Component.PK types which are sub-types of PublishableEntity.PK
Container and Component cannot have correctly-typed .pk accessors due to django-stubs limitations, so I created a .container_pk and .component_pk accessor for them:
- Details: because Container and Component have a OneToOneField(PublishsableEntity, primary_key=True), django-stubs will always override their pk attribute to have type Any, and it's impossible to change this without modifying django-stubs or writing our own mypy plugin. But, we can use the @deprecated decorator to annotate the attribute with a deprecation warning which does show up in the IDE and in the pytest logs wherever .pk is used.
- I think this is clear and explicit, but would something shorter be better (.pk_ ?)

General Notes

One downside of using deprecation warnings as I have here is that Django itself uses .pk, so in the case of Container and Component (but not PublishableEntity) where we've marked .pk as deprecated, even if our code doesn't use .pk itself, you'll see warnings like this when running pytest: django/db/models/fields/related.py:812: DeprecationWarning: Use component_pk instead. It is possible to suppress these deprecation warnings, and I have done so (see tox.ini) but it's an extra step required to use this library well and I'm not a big fan of it.

openedx-webhooks · 2026-04-07T18:29:30Z

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bradenmacdonald · 2026-04-07T20:03:09Z

@ormsbee @kdmccormick Can I get your thoughts on this? It also has implications for OEP-68.

ormsbee · 2026-04-07T21:18:09Z

src/openedx_content/applets/components/models.py

+        # Note: Django-Stubs forces mypy to identify the `.pk` attribute of this model as having 'Any' type (due to our
+        # use of a OneToOneField primary key), and this is impossible for us to override, so we prefer to use
+        # `.id` which we can control fully.
+        # Since Django uses '.pk' internally, we have to make sure it still works, however. So the best we can do is
+        # override this with a deprecated marker, so it shows a warning in developer's IDEs like VS Code.


Ouch. Very timely to know this given the OEP in flight on identifiers, where we recommend using .pk.

Yes, as you can read above in the edited description, I actually changed my approach here, as it turns out it's much easier to override the type of .id than .pk in general. So I'm wondering if we should just recommend .id / _id more.

oof, good find. I've opened a thread here: openedx/openedx-proposals#773 (comment)

If we standardize on .id, then I presume we can drop this deprecation warning? I think most developers naturally use .id anyway.

I found that .pk was being used in quite a few places in this codebase, and the deprecation warnings made it easy for me to track them down and replace them with .id.

src/openedx_content/applets/publishing/models/id_fields.py

bradenmacdonald · 2026-04-08T17:47:06Z

If we want to also introduce typed keys for Unit/Section/Subsection subclasses, that's easy to do: #535 . Would welcome thoughts on this as I'm a bit on the fence.

src/openedx_content/applets/containers/models.py

bradenmacdonald · 2026-04-08T23:16:44Z

OK, good news! I found a nicer way to do this. It still requires a custom field type per model, but we can put the definitions entirely within the model class itself, and there is now one global id_fields module in openedx_django_lib rather than needing id_fields.py and id_fields.pyi alongside each app[let]'s models.

e.g. within the class LearningPackage(models.Model): definition:

openedx-core/src/openedx_content/applets/publishing/models/learning_package.py

Lines 32 to 38 in 959f9e6

    
           LearningPackageID = NewType("LearningPackageID", int) 
        
           type ID = LearningPackageID 
        
           class IDField(TypedBigAutoField[ID]): 
        
               pass 
        
           id = IDField(primary_key=True)

Note:

This could be made even more concise, and copy-pastable without changes:

ID = NewType("ID", int) 
class IDField(TypedBigAutoField[ID]): ...
id = IDField(primary_key=True)

But: this creates ambiguous type names (what is "ID", without context?) in the mypy output, and the use of an ellipsis instead of pass implies that something is incomplete. So I'm recommending the more verbose version as our new standard boilerplate.

Edit: actually this works great, so I think I prefer the second version now. If you have several types called ID, mypy distinguished them in the output like so:

error: Argument 1 to "update_learning_package" has incompatible type
"openedx_content.applets.publishing.models.learning_package.LearningPackage.ID"; expected
"openedx_content.applets.publishing.models.publishable_entity.PublishableEntity.ID"  [arg-type]

kdmccormick · 2026-04-09T15:39:54Z

@bradenmacdonald woohoo! The TypedBigAutoField is a huge improvement. I was fiddling with my own version of TypedBigAutoField last night and decided that it must be impossible :P Nice work on the __class_getitem__ hack.

Edit: actually this works great, so I think I prefer the second version now. If you have several types called ID, mypy distinguished them in the output like so:
error: Argument 1 to "update_learning_package" has incompatible type
"openedx_content.applets.publishing.models.learning_package.LearningPackage.ID"; expected
"openedx_content.applets.publishing.models.publishable_entity.PublishableEntity.ID"  [arg-type]

I'm a little iffy on this--this is a pretty painful error message to read. I think I'd prefer more boilerplate in exchange for more-legible messages:

error: Argument 1 to "update_learning_package" has incompatible type LearningPackageID; expected PublishableEntityID  [arg-type]

bradenmacdonald · 2026-04-09T16:36:19Z

@kdmccormick OK, good call. I changed that back. It now looks like: error: Argument 1 to "get_entities_with_unpublished_changes" has incompatible type "LearningPackageID"; expected "PublishableEntityID" [arg-type]

kdmccormick

LGTM , just one question about next steps.

EDIT: GitHub lost my comment 🤦🏻 I'll rewrite it after my meeting....

bradenmacdonald · 2026-04-09T17:54:37Z

@kdmccormick Here is the corresponding platform PR which shows the required changes (pretty minimal) plus demonstrates using the new field to make StagedContent also use fully-typed IDs.

openedx/openedx-platform#38308

kdmccormick · 2026-04-09T18:01:02Z

src/openedx_django_lib/id_fields.py

+        MyModelID = NewType("MyModelID", int)
+        type ID = MyModelID
+
+        class IDField(TypedBigAutoField[ID]):
+            pass
+
+        id = IDField(primary_key=True)


Not for this PR, but as a possible followup: at the expense of some more boilerplate, what do you think about extending this same system to model relationships?

Suggested change

MyModelID = NewType("MyModelID", int)

type ID = MyModelID

class IDField(TypedBigAutoField[ID]):

pass

id = IDField(primary_key=True)

# Boilerplate for strongly-typed model relationships.

# Replace "MyModel" with your model's name.

MyModelID = NewType("MyModelID", int)

type ID = MyModelID

class IDField(TypedBigAutoField[ID]):

pass

class ForeignKey(TypedForeignKey[ID]):

def __init__(self, *args, **kwargs):

super().__init__("MyModel", *args, **kwargs)

class OneToOneField(TypedOneToOneField[ID])

def __init__(self, *args, **kwargs):

super().__init__("MyModel", *args, **kwargs)

id = IDField(primary_key=True)

# To make references to other strongly-typed models:

my_related_object = MyOtherModel.ForeignKey(on_delete=..., ...)

my_one_to_one_object = MyAdditionalModel.OneToOneField(on_delete=..., ...)

# etc.

maybe there's even some way to shove super().__init__("MyModel", *args, **kwargs) into TypedForeignKey/TypedOneToOneField, so the body of all three field classes can be pass.

@kdmccormick It's not necessary! The django-stubs plugin should already be providing the correct types for all the foreign key _id fields 😎

Please let me know if you observe any exceptions or if I'm wrong.

bradenmacdonald · 2026-04-09T19:18:21Z

src/openedx_content/migrations/0006_typed_ids.py

+                migrations.AlterField(
+                    model_name="publishableentity",
+                    name="id",
+                    field=models.BigAutoField(primary_key=True, serialize=False),


Just noting here that changing to these fully-typed primary keys does not result in any migration if the model previous had an explicit id field. But if it had only the implicit, auto-created field, then adding an explicit one results in this kind of migration. By default such migrations will re-create the table in order to re-create the ID column, even though nothing has changed, so it's important to catch that and tweak the migration like this to not actually make any DB changes.

bradenmacdonald · 2026-04-09T20:30:41Z

I made two final tiny fixes as a result of testing this in openedx-platform: 085393d and bd68671 . I'm going to squash this now to get all the checks passing.

feat: added typed primary keys for Container feat: added typed primary keys for Component feat: added typed primary keys for PublishableEntity feat: added typed primary keys for LearningPackage feat: added typed primary keys for CatalogCourse and CourseRun feat: added typed primary keys for Units/Subsections/Sections refactor: change typed ID fields to use 'id' instead of 'pk' feat: add a default 'id' accessor to PublishableEntityMixin

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docs: OEP-68 Learning Content Identifiers openedx/openedx-proposals#773

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feat: typed PK identifiers for Units/Subsections/Sections #535

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bradenmacdonald force-pushed the braden/typed-pks branch from 9d0d7c4 to cd54e54 Compare April 9, 2026 00:07

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bradenmacdonald changed the title ~~Add type annotations for primary key types by model~~ Add type annotations for primary key types by model [FC-0117] Apr 9, 2026

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Platform: Add type annotations for primary key types by model [FC-0117] openedx/openedx-platform#38308

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bradenmacdonald force-pushed the braden/typed-pks branch from bd68671 to 96343db Compare April 9, 2026 20:33

-        MyModelID = NewType("MyModelID", int)
-        type ID = MyModelID
-        class IDField(TypedBigAutoField[ID]):
-            pass
-        id = IDField(primary_key=True)
+        # Boilerplate for strongly-typed model relationships.
+        # Replace "MyModel" with your model's name.
+        MyModelID = NewType("MyModelID", int)
+        type ID = MyModelID
+        class IDField(TypedBigAutoField[ID]):
+            pass
+        class ForeignKey(TypedForeignKey[ID]):
+            def __init__(self, *args, **kwargs):
+                super().__init__("MyModel", *args, **kwargs)
+        class OneToOneField(TypedOneToOneField[ID])
+            def __init__(self, *args, **kwargs):
+                super().__init__("MyModel", *args, **kwargs)
+        id = IDField(primary_key=True)
+        # To make references to other strongly-typed models:
+        my_related_object = MyOtherModel.ForeignKey(on_delete=..., ...)
+        my_one_to_one_object = MyAdditionalModel.OneToOneField(on_delete=..., ...)
+        # etc.

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Second Approach: fully-typed .id, avoid .pk

Prior Approach: fully-typed .pk, avoid .id

General Notes

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Second Approach: fully-typed `.id`, avoid `.pk`

Prior Approach: fully-typed `.pk`, avoid `.id`

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