`use_database_state` hook

[Archmonger]

Old Behavior

State is generated on a per-render basis and has no method of being permanently stored.

Additionally, there is no convenient way to perform DB queries within components (as of Django 4.1)

New Behavior

Allow for persistent state that is databased backed.

Implementation Details

Persistently store/restore context based on a database model.

The interface should take in a single database object...

from my_django_app.models import GeneralSettings

state, set_state = hooks.use_database_state(GeneralSettings.objects.get(id=20))
state.my_database_field = True

# This saves the values to the database and issues a re-render.
set_state(state)

In the background, the set state is doing the following...

def set_state(state):
    state.save()
    ...

Code of Conduct

• I agree to follow the Code of Conduct.

[rmorshea]

I imagine the usage should look like either:

results = use_database(lambda: Model.objects.all())

@use_database
def results():
    return Model.objects.all()

The implementation might look like:

def use_database(function, initial_value=None):
    result, set_result = use_state(initial_value)

    query_function = use_callback(query_function)
    async_function = use_memo(lambda: database_sync_to_async(function))

    @use_effect
    async def exec_function():
        output = await async_function()
        if isinstance(output, QuerySet):
            bool(output)
        set_result(output)

    return result

[Archmonger]

With that kind of interface, how would someone edit an entry and then save changes?

There needs to be some way of performing .save() operations via database_sync_to_async

[rmorshea]

Wouldn't one typically do that in response to some sort of event, in which case you'd be able to define an async handler that does this?

[rmorshea]

You're right though, that does feel a bit disjointed. Maybe the interface ought to be more like use_state for single record access.

model, set_model = use_one_model(
    Model.objects.get(...)  # assuming query exec is delayed
)

async def handle_event():
    await set_model(attr=...)

[rmorshea]

I'm not really sure how this should work for bulk access though...

[rmorshea]

Actually, there's a deeper issue here around object identity where the declarative nature of IDOM and the imperative nature of Django clash - Django expects you to modify an object to update it in the database, but IDOM uses object identity to infer whether something has changed. For example, imagine using a model in a use_memo hook:

model, set_model = use_one_model(...)
something_expensive = use_memo(lambda: compute_something_expensive(model))

A naive implementation of use_one_model would mutate model, call model.save() and, on the next render, return the same model instance. But in order to know whether something_expensive needs to be re-computed, IDOM looks at the identity of model. If model is the same object, then something_expensive won't be re-computed. Thus you'd encounter a bug where, despite calling set_model, something_expensive would not receive a corresponding update.

It almost feels like there needs to be a thin declarative wrapper around Django's models...