如何在更新django表单时自动填充字段？

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

class MyForm(forms.ModelForm):
    class Meta:
        model = MyModel
        fields = ['field1', 'field2', 'field3']
    
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        instance = kwargs.get('instance')
        if instance:
            self.initial['field1'] = instance.field1  # 自动填充field1的初始值
            # 可以继续添加其他字段的初始值

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

def update_model(request, pk):
    instance = MyModel.objects.get(pk=pk)
    if request.method == 'POST':
        form = MyForm(request.POST, instance=instance)
        if form.is_valid():
            form.save()
            # 处理表单提交成功后的逻辑
    else:
        form = MyForm(instance=instance)
    return render(request, 'update.html', {'form': form})

# update.html
<form method="post" action="{% url 'update_model' pk=instance.pk %}">
  {% csrf_token %}
  {{ form.as_p }}
  <button type="submit">保存</button>
</form>