Detect underlying field for OneToOne primary key

[schferbe]

Description

When using a OneToOneField as a primary key it does not get serialized in the same way as the "parent" model. E.g.

        class MyModelA(models.Model):
            id = models.DecimalField(max_digits=4, decimal_places=2, primary_key=True)

        class MyModelB(models.Model):
            id = models.OneToOneField(MyModelA, models.CASCADE, primary_key=True)

        class MyModelASerializer(serializers.ModelSerializer):
            class Meta:
                model = MyModelA
                fields = "__all__"

        class MyModelBSerializer(serializers.ModelSerializer):
            class Meta:
                model = MyModelB
                fields = "__all__"

The following serializations would result

MyModelASerializer().to_representation(MyModelA(id=12.34))
# {"id": "12.24"}
MyModelBSerializer().to_representation(MyModelB(id=MyModelA(id=12.34)))
# {"id": 12.24}

This PR sets the pk_field attribute of the PrimaryKeyRelatedField to ensure serialization is consistent with the "parent" model. This is also in line with the OpenApi schema that would be generated.

[schferbe]

Should the field_name be extracted from the foreign_related_fields[0] here?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[schferbe]

bump

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[schferbe]

bump

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[tomchristie]

Okay - I think this makes sense.(?)

Is there an example that's more obvious than a DecimalField pk?
Feels pretty confusing using a Decimal as a primary key.

[auvipy]

decimal field as primary key? what are some actual use case of that?

[auvipy]

instead o using decimal field as primary key, can you try something else like UUID field as primary key here in test case?