使用实例编辑django表单始终加载空表单域

form = MyForm(request.POST or None, instance=my_instance)

# forms.py
from django import forms
from .models import MyModel

class MyForm(forms.ModelForm):
    class Meta:
        model = MyModel
        fields = ['field1', 'field2', 'field3']

# views.py
from django.shortcuts import render, redirect
from .forms import MyForm
from .models import MyModel

def edit_form(request, pk):
    my_instance = MyModel.objects.get(pk=pk)
    form = MyForm(request.POST or None, instance=my_instance)
    
    if request.method == 'POST':
        if form.is_valid():
            form.save()
            return redirect('success')
    
    return render(request, 'edit_form.html', {'form': form})

# edit_form.html
<form method="POST">
    {% csrf_token %}
    {{ form.field1 }}
    {{ form.field2 }}
    {{ form.field3 }}
    <button type="submit">Save</button>
</form>