# forms.py
from django import forms

class MyForm(forms.Form):
    # 定义表单字段
    my_field = forms.CharField(label='主键')

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

def my_view(request):
    if request.method == 'POST':
        form = MyForm(request.POST)
        if form.is_valid():
            # 获取用户输入的主键
            primary_key = form.cleaned_data['my_field']
            try:
                # 查询数据库
                obj = MyModel.objects.get(pk=primary_key)
                # 填充数据到表单
                form = MyForm(initial={'my_field': obj.my_field})
                # 在context中返回填充后的表单和其他数据
                context = {'form': form, 'obj': obj}
                return render(request, 'my_template.html', context)
            except MyModel.DoesNotExist:
                # 处理主键不存在的情况
                form.add_error('my_field', '该主键不存在')
    else:
        form = MyForm()

    return render(request, 'my_template.html', {'form': form})