Django FormSets是否支持对FileFields字段进行预填充？

1 修复上下文变量名冲突问题 #

你当前代码在get方法中构造了带初始值的procedure_attachment_form并传入模板，但get_context_data方法里又将context["attachments"]赋值为空表单集，且模板引用的变量名是procedure_attachment_form，二者不匹配导致初始值完全失效。
修改get_context_data方法：

def get_context_data(self, **kwargs):
    context = super(UpdateProcedureView, self).get_context_data(**kwargs)
    # 移除原有重复构造表单集的逻辑，不要覆盖get方法传入的procedure_attachment_form
    return context

同时将inlineformset_factory的定义移到类视图外部或类变量位置，避免每次请求重复构造：

# 类视图外定义
UpdateProcedureFileFormSet = inlineformset_factory(
    UpdateProcedure,
    UpdateProcedureFiles,
    form=UpdateProcedureFilesForm,
    can_delete=True, # 开启删除功能，满足审核后删除附件的需求
    can_order=True,
    min_num=0,
    validate_min=True
)

2 解决FileField无法预填充的展示问题 #

浏览器安全限制禁止给文件上传框预设值，你需要单独渲染已有附件的信息，修改HTML模板：

{% for fileform in procedure_attachment_form.forms %}
{{ fileform.id }}
<div class="inline {{ procedure_attachment_form.prefix }}">
    <!-- 新增：展示已有附件 -->
    {% if fileform.instance.attachments %}
        <p>已上传附件：<a href="{{ fileform.instance.attachments.url }}" target="_blank">{{ fileform.instance.attachments.name }}</a></p>
        <!-- 隐藏字段存储原有附件路径，用于后续复制到新模型 -->
        <input type="hidden" name="existing_attachments[]" value="{{ fileform.instance.attachments.name }}">
        {{ fileform.DELETE }} <!-- 渲染删除勾选框，支持删除已有附件 -->
    {% endif %}
    {{ fileform.attachments }}
    {% if procedure_attachment_form.non_form_errors %}
        <h3 class="spacer174">
            {{ procedure_attachment_form.non_form_errors }}
        </h3>
    {% endif %}
    {% if fileform.attachments.errors %}
        <h3 class="spacer174">
            {{ fileform.attachments.errors }}
        </h3>
    {% endif %}
    {{ fileform.procedure.as_hidden }}
</div>
{% endfor %}

同时修改表单，移除multiple=True配置，避免和表单集逻辑冲突：

class UpdateProcedureFilesForm(forms.ModelForm):
    class Meta:
        model = UpdateProcedureFiles
        fields = ['attachments', 'DELETE'] # 新增DELETE字段支持删除
        widgets = {
            'attachments': ClearableFileInput(), # 移除multiple属性
        }

3 修复提交时附件处理逻辑 #

你当前post方法只处理了新上传的文件，新增原有附件的复制逻辑：

def post(self, request, *args, **kwargs):
    if "cancel" in request.POST:
        return HttpResponseRedirect(reverse('Procedures:procedure_main_menu'))
    else:
        self.object = None
        form_class = self.get_form_class()
        form = self.get_form(form_class)
        procedure_attachment_form = UpdateProcedureFileFormSet(self.request.POST,self.request.FILES)
        if (form.is_valid() and procedure_attachment_form.is_valid()):
            procedure_instance = form.save(commit=False)
            procedure_instance.user = request.user
            procedure_instance.save()
            
            # 保存表单集的新上传文件
            procedure_attachment_form.instance = procedure_instance
            procedure_attachment_form.save()
            
            # 处理原有附件复制：从hidden字段取已有附件路径，复制到新模型
            existing_attachments = request.POST.getlist('existing_attachments[]')
            for i, attach_path in enumerate(existing_attachments):
                # 检查该附件是否被勾选删除，未删除则复制
                delete_check = request.POST.get(f'{procedure_attachment_form.prefix}-{i}-DELETE', None)
                if not delete_check:
                    # 从原有模型取附件对象
                    old_attach = ProcedureFiles.objects.filter(attachments=attach_path).first()
                    if old_attach:
                        # 直接复制FieldFile到新模型
                        UpdateProcedureFiles.objects.create(
                            attachments=old_attach.attachments,
                            update_procedure=procedure_instance
                        )
            return self.form_valid(form, procedure_attachment_form)
        else:
            return self.form_invalid(form, procedure_attachment_form)

4 补充初始值构造逻辑 #

修改get方法中表单集的初始化参数，传入queryset而非initial，更适配已有数据的渲染：

def get(self, request, *args, **kwargs):
    self.object = self.get_object()
    form = self.get_form()
    dropdown = self.kwargs["pk"]
    attachments = ProcedureFiles.objects.filter(procedure_id=dropdown)

    # 传入queryset渲染已有附件，extra控制新增空白输入框的数量
    procedure_attachment_form = UpdateProcedureFileFormSet(
        queryset=attachments,
        extra=1 # 留一个空白输入框用于上传新附件
    )

    return self.render_to_response(
        self.get_context_data(
            form=form,
            procedure_attachment_form=procedure_attachment_form,
        )
    )

内容的提问来源于stack exchange，提问作者Steve Smith