Are nested dataclasses form submissions supported?

[iamyojimbo]

When posting form data to an endpoint and using that to populate a dataclass, are nested data classes supported?

I can make the below, self-contained example work like this:

@dataclass()
class State:
    x: int = 1
    y: int = 2

    def __ft__(self):
        return ft.Form(
            ft.Input(name="x", type="number", value=self.x),
            ft.Input(name="y", type="number", value=self.y),
            ft.Pre(self.serialise(), id="state_json"),
            hx_post="/",
            hx_target="#state_json",
            hx_trigger="change from:input delay:200ms",
            hx_sync="this:replace",
        )

    def serialise(self):
        return json.dumps(asdict(self))

@app.post("/")
def _(state: State):
    return state.serialise()

but I can't find a configuration to make it work when adding a nested property to State, which is also a dataclass. Here's the full example:

import json
import fasthtml.common as fc
from fasthtml import ft
from dataclasses import asdict, dataclass, field

app, rt = fc.fast_app(
    debug=True,
    live=True,
)


@dataclass
class Nested:
    a: int = 3
    b: int = 4

    def __ft__(self):
        return ft.Div(
            ft.Input(name="a", type="number", value=self.a),
            ft.Input(name="b", type="number", value=self.b),
        )


@dataclass()
class State:
    x: int = 1
    y: int = 2
    nested: Nested = field(default_factory=Nested)

    def __ft__(self):
        return ft.Form(
            ft.Input(name="x", type="number", value=self.x),
            ft.Input(name="y", type="number", value=self.y),
            Nested(),
            ft.Pre(self.serialise(), id="state_json"),
            hx_post="/",
            hx_target="#state_json",
            hx_trigger="change from:input delay:200ms",
            hx_sync="this:replace",
        )

    def serialise(self):
        return json.dumps(asdict(self))


@app.get("/")
def _():
    return State()


@app.post("/")
def _(state: State):
    return state.serialise()


fc.serve()

When changing any of the nested fields, a and b, the JSON updates, but always has the initial values 3 and 4. Is there any way to also have those be supported. Looking at the source here, I assume not, because fill_dataclass is not recursive.

Thanks for the awesome library, and thanks in advance for any help!