Access properties and functions in templates

[themagiulio]

Is there a way to access properties and functions inside a template?

Let's say I have the following model:

class Group(models.Model):
    ...
    members = models.ManyToManyField(User)

    @property
    def full_name(self):
        return f"{self.name}#{self.identifier}"

I would like to render in React the full_name of Group and the result of members.count(). Ideally I would like to do something like that:

@template
class Group(NamedTuple):
   name: Pick[Group, "full_name", "members.count"]

[silviogutierrez]

@themagiulio : there is! You can "Pick" anything marked as "property". It should Just Work™.

[themagiulio]

That's what I thought, but it does not seem to work. In both cases I get a key error.

When I try to access a property:
django.core.exceptions.FieldDoesNotExist: Model has no field named 'full_name'

When I try to reference a function:
django.core.exceptions.FieldDoesNotExist: Model has no field named 'count'

[themagiulio]

Oh, I just found the issue! Those functions didn't have a return type 🤦‍♂️
Unfortunately the count function doesn't have types, so I have to re-implement the method.

Thank you so much!

[silviogutierrez]

I want to add count support as I find myself writing members_count and similar methods a lot.

One question: you do need annotations for this to work, as you noticed. But the error doesn't make sense. You should be getting a key error here:

reactivated/reactivated/pick.py

Line 84 in 6922107

annotation=annotations["return"],

for return.

But not for a field does not exist. There's even a test for it here:

reactivated/tests/serialization.py

Line 58 in 6922107

pick_property: Pick[models.Composer, "did_live_in_more_than_one_country"]

If you look at the model and comment out the return annotation, you get KeyError for return. Not FieldDoesNotExist.

Any idea why you're getting the wrong error?

[themagiulio]

Support for count would be great indeed!

To reply to your question, as you said I get a KeyError. However, the end of the error output states it is a FieldDotesNotExist.

I leave the error output for reference:

Traceback (most recent call last):
  File "/project_dir/.venv/lib/python3.9/site-packages/django/db/models/options.py", line 608, in get_field
    return self.fields_map[field_name]
KeyError: 'count'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/project_dir/manage.py", line 22, in <module>
    main()
  File "/project_dir/manage.py", line 18, in main
    execute_from_command_line(sys.argv)
  File "/project_dir/.venv/lib/python3.9/site-packages/django/core/management/__init__.py", line 425, in execute_from_command_line
    utility.execute()
  File "/project_dir/.venv/lib/python3.9/site-packages/django/core/management/__init__.py", line 419, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/project_dir/.venv/lib/python3.9/site-packages/django/core/management/base.py", line 373, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/project_dir/.venv/lib/python3.9/site-packages/django/core/management/commands/runserver.py", line 66, in execute
    super().execute(*args, **options)
  File "/project_dir/.venv/lib/python3.9/site-packages/django/core/management/base.py", line 417, in execute
    output = self.handle(*args, **options)
  File "/project_dir/.venv/lib/python3.9/site-packages/django/core/management/commands/runserver.py", line 101, in handle
    self.run(**options)
  File "/project_dir/.venv/lib/python3.9/site-packages/django/core/management/commands/runserver.py", line 108, in run
    autoreload.run_with_reloader(self.inner_run, **options)
  File "/project_dir/.venv/lib/python3.9/site-packages/django/utils/autoreload.py", line 646, in run_with_reloader
    exit_code = restart_with_reloader()
  File "/project_dir/.venv/lib/python3.9/site-packages/reactivated/__init__.py", line 45, in patched_restart_with_reloader
    schema = get_schema()
  File "/project_dir/.venv/lib/python3.9/site-packages/reactivated/apps.py", line 132, in get_schema
    "types": get_types_schema(),
  File "/project_dir/.venv/lib/python3.9/site-packages/reactivated/apps.py", line 94, in get_types_schema
    parent_schema, definitions = create_schema(ParentTuple, definitions_registry)
  File "/project_dir/.venv/lib/python3.9/site-packages/reactivated/serialization/__init__.py", line 787, in create_schema
    return named_tuple_schema(Type, definitions)
  File "/project_dir/.venv/lib/python3.9/site-packages/reactivated/serialization/__init__.py", line 725, in named_tuple_schema
    field_schema = create_schema(Subtype, definitions)
  File "/project_dir/.venv/lib/python3.9/site-packages/reactivated/serialization/__init__.py", line 787, in create_schema
    return named_tuple_schema(Type, definitions)
  File "/project_dir/.venv/lib/python3.9/site-packages/reactivated/serialization/__init__.py", line 725, in named_tuple_schema
    field_schema = create_schema(Subtype, definitions)
  File "/project_dir/.venv/lib/python3.9/site-packages/reactivated/serialization/__init__.py", line 781, in create_schema
    return Type.get_json_schema(definitions)  # type: ignore[no-any-return]
  File "/project_dir/.venv/lib/python3.9/site-packages/reactivated/pick.py", line 280, in get_json_schema
    field_descriptor, path = get_field_descriptor(
  File "/project_dir/.venv/lib/python3.9/site-packages/reactivated/pick.py", line 105, in get_field_descriptor
    nested_descriptor, nested_field_names = get_field_descriptor(
  File "/project_dir/.venv/lib/python3.9/site-packages/reactivated/pick.py", line 88, in get_field_descriptor
    raise e
  File "/project_dir/.venv/lib/python3.9/site-packages/reactivated/pick.py", line 60, in get_field_descriptor
    descriptor=model_class._meta.get_field(field_name),
  File "/project_dir/.venv/lib/python3.9/site-packages/django/db/models/options.py", line 610, in get_field
    raise FieldDoesNotExist("%s has no field named '%s'" % (self.object_name, field_name))
django.core.exceptions.FieldDoesNotExist: User has no field named 'count'

[silviogutierrez]

Got it. Sounds like that newish Python feature where they show you both, the inner exception and the outer exception. Forget which version added this.