Pick doesn't serialise ids correctly for nested model properties

[kyczawon]

I found an issue with serialisation where parent id overrides children ids during serialisation.

Example

Assume I have the following 2 models and a property in the parent which extract data from the child:

class ChildInfo(TypedDict):
    id: str
    description: str

class ParentModel(models.Model):
   @property
    def children_info(self) -> List[ChildInfo]:
        children = ChildModel.objects.filter(parent__pk=self.id)
        return [ChildInfo(id=child.id, description=child.description) for child in children]

class ChildModel(models.Model):
    parent = models.ForeignKey(
        to=Parent,
        verbose_name="linked [parent",
    )

    description = models.TextField()

Template:

@template
class View(NamedTuple):
    parent: Pick[models. ParentModel, "id", "children_info"]

Now assume I have ParentModel (id:1) linked to two ChildModels (id:20 & id: 25)

When I print children_info on django side I get the ids as expected:

[{'id': 20, 'description': 'test'}, {'id': 25, 'description': 'test2'}]

However, on client side the parent id overrides the children ids:

{
'id': 1,
'children_info': [{'id': 1, 'description': 'test'}, {'id': 1, 'description': 'test2'}]
}

Temporary Fix

Changing the definition of ChildInfo fixed the issue:

class ChildInfo(TypedDict):
    version_id: str
    description: str

And I correctly get the same output on both django and client side:

[{'version_id': 20, 'description': 'test'}, {'version_id': 25, 'description': 'test2'}]

Question

Is there an issue with serialisation when a name clash between ids happens?

[silviogutierrez]

That's nuts, I can't even imagine why it would happen. You're not going through the Pick layer for the ChildInfo. You're manually instantiating it. So I have no explanation.

Should be pretty easy to reproduce with a test in tests/serialization.py. See if you can take a stab then just run pytest.

[kyczawon]

Realised that my design was probably flawed here. Instead I opted to use pick on the child and do the query on the view & this bug doesn't happen there:

@template
class View(NamedTuple):
    parent: Pick[models. ParentModel, "id", "children_info"]
    children: List[Pick[models. childModel, "id", "description"]]

And then doing the fetch within the view:

parent = get_object_or_404(
        models.ParentModel, org=request.user.current_org, id=prompt_id
    )
children = get_list_or_404(
        models.ChildModel, parent=parent
    )
return templates.View(
        parent=parent,
        children=children,
    ).render(request)

[silviogutierrez]

You can also just do the reverse relationship, far easier:

Add related_name="children" to the parent = models.ForeignKey declaration. See https://docs.djangoproject.com/en/5.0/ref/models/fields/#django.db.models.ForeignKey.related_name

Then just pick right at the parent level:

Pick[models. ParentModel, "id", "children.id", "children.description"]

And you only need to load the parent and pass it to the template. Magic!

PS. Technically you don't need a related name, just childmodel_set already exists on the parent model. But I don't like that name as much.