form_utils.py

from functools import wraps

from django.forms import Form
from django.http import HttpResponse


def htmx_form_validate(*, form_class: type):
    """
    Instead of a normal view, just do htmx validation using the given form class,
    for a single field and return the single div that needs to be replaced.
    Normally the form class will be the same class used in the view body.
    """

    def decorator(view_func):
        @wraps(view_func)
        def wrapper(request, *args, **kwargs):
            if (
                request.method == "GET"
                and "Hx-Request" in request.headers
                and (htmx_validation_field := request.GET.get("_validate_field", None))
            ):
                form = form_class(request.GET)
                form.is_valid()  # trigger validation
                return HttpResponse(render_single_field_row(form, htmx_validation_field))
            return view_func(request, *args, **kwargs)

        return wrapper

    return decorator


def render_single_field_row(form: Form, field_name: str):
    # Assumes form has renderer with `single_field_row_template` defined
    bound_field = form[field_name]
    return form.render(
        context={
            "field": bound_field,
            "errors": form.error_class(bound_field.errors, renderer=form.renderer),
            "do_htmx_validation": form.do_htmx_validation,
        },
        template_name=form.renderer.single_field_row_template,
    )