使用ModelForms时如何更新现有行？

from django.shortcuts import get_object_or_404
from .models import MyModel

def update_row(request, id):
    my_object = get_object_or_404(MyModel, id=id)

from .forms import MyModelForm

def update_row(request, id):
    my_object = get_object_or_404(MyModel, id=id)
    form = MyModelForm(request.POST or None, instance=my_object)

from django.shortcuts import redirect

def update_row(request, id):
    my_object = get_object_or_404(MyModel, id=id)
    form = MyModelForm(request.POST or None, instance=my_object)

    if form.is_valid():
        form.save()
        return redirect('some_view')

<form method="post">
    {% csrf_token %}
    {{ form.as_p }}
   <button type="submit">Update</button>
</form>