使用基于类的视图处理表单-未完纪

表单处理通常有三条路径：

初始 GET 请求：显示空白表单或预填充表单。
携带无效数据的 POST 请求：通常重新显示表单及错误。
携带有效数据的 POST 请求：处理数据，通常随后重定向。

自己实现这些流程会产生大量重复样板代码，参见在视图中使用表单。Django 提供了一组处理表单的通用基于类的视图来避免这个问题。

基础表单

假设有下面的联系表单，定义在 forms.py：

from django import forms


class ContactForm(forms.Form):
    name = forms.CharField()
    message = forms.CharField(widget=forms.Textarea)

    def send_email(self):
        # send email using the self.cleaned_data dictionary
        pass

可以使用 FormView 构建视图，views.py：

from myapp.forms import ContactForm
from django.views.generic.edit import FormView


class ContactFormView(FormView):
    template_name = "contact.html"
    form_class = ContactForm
    success_url = "/thanks/"

    def form_valid(self, form):
        # This method is called when valid form data has been POSTed.
        # It should return an HttpResponse.
        form.send_email()
        return super().form_valid(form)

注意：

FormView 继承 TemplateResponseMixin，因此可使用 template_name。
默认的 form_valid() 实现只是重定向到 success_url。

模型表单

与模型一起使用时，通用视图尤为便利。只要能确定模型类，它们就会自动创建 ModelForm：

如果给出了 model 属性，就使用这个模型类。
如果 get_object() 返回一个对象，就使用该对象所属的类。
如果给出了 queryset，就使用该查询集的模型。

模型表单视图提供会自动保存模型的 form_valid() 实现。有特殊需求时可以覆盖它，下文提供了示例。

如果模型对象提供了 get_absolute_url()，那么 CreateView 和 UpdateView 会使用它，你甚至不必设置 success_url。

需要自定义 ModelForm，例如增加验证时，在视图上设置 form_class。指定自定义表单类时仍必须指定模型，即使 form_class 本身就是一个 ModelForm。

首先，为 Author 添加 get_absolute_url()，models.py：

from django.db import models
from django.urls import reverse


class Author(models.Model):
    name = models.CharField(max_length=200)

    def get_absolute_url(self):
        return reverse("author-detail", kwargs={"pk": self.pk})

然后让通用视图完成实际工作。下面的配置无需自己编写处理逻辑，views.py：

from django.urls import reverse_lazy
from django.views.generic.edit import CreateView, DeleteView, UpdateView
from myapp.models import Author


class AuthorCreateView(CreateView):
    model = Author
    fields = ["name"]


class AuthorUpdateView(UpdateView):
    model = Author
    fields = ["name"]


class AuthorDeleteView(DeleteView):
    model = Author
    success_url = reverse_lazy("author-list")

这里必须用 reverse_lazy() 而非 reverse()，因为导入文件时 URL 尚未加载。

fields 的作用与 ModelForm 内部 Meta 类的 fields 属性相同。除非通过其他方式定义表单类，否则必须提供该属性；缺少它会引发 ImproperlyConfigured。同时指定 fields 和 form_class 也会引发该异常。

最后，在 URLconf 中连接这些视图，urls.py：

from django.urls import path
from myapp.views import AuthorCreateView, AuthorDeleteView, AuthorUpdateView

urlpatterns = [
    # ...
    path("author/add/", AuthorCreateView.as_view(), name="author-add"),
    path("author/<int:pk>/", AuthorUpdateView.as_view(), name="author-update"),
    path("author/<int:pk>/delete/", AuthorDeleteView.as_view(), name="author-delete"),
]

这些视图继承 SingleObjectTemplateResponseMixin，后者使用 template_name_suffix 构造基于模型的 template_name。本例中：

CreateView 和 UpdateView 使用 myapp/author_form.html。
DeleteView 使用 myapp/author_confirm_delete.html。

如需让 CreateView 和 UpdateView 使用不同模板，可在视图类上设置 template_name 或 template_name_suffix。

模型与 `request.user`

要跟踪哪个用户通过 CreateView 创建了对象，可以使用自定义 ModelForm。先为模型添加外键关系，models.py：

from django.contrib.auth.models import User
from django.db import models


class Author(models.Model):
    name = models.CharField(max_length=200)
    created_by = models.ForeignKey(User, on_delete=models.CASCADE)

    # ...

在视图中，确保 created_by 不在可编辑字段列表内，并覆盖 form_valid() 来添加用户，views.py：

from django.contrib.auth.mixins import LoginRequiredMixin
from django.views.generic.edit import CreateView
from myapp.models import Author


class AuthorCreateView(LoginRequiredMixin, CreateView):
    model = Author
    fields = ["name"]

    def form_valid(self, form):
        form.instance.created_by = self.request.user
        return super().form_valid(form)

LoginRequiredMixin 会阻止未登录用户访问表单。若省略该混入，就需要在 form_valid() 中自行处理未授权用户。

内容协商示例

下面的示例展示如何同时支持 API 工作流与普通 POST 表单：

from django.http import JsonResponse
from django.views.generic.edit import CreateView
from myapp.models import Author


class JsonableResponseMixin:
    """
    Mixin to add JSON support to a form.
    Must be used with an object-based FormView (e.g. CreateView)
    """

    def form_invalid(self, form):
        response = super().form_invalid(form)
        if self.request.accepts("text/html"):
            return response
        else:
            return JsonResponse(form.errors, status=400)

    def form_valid(self, form):
        # We make sure to call the parent's form_valid() method because
        # it might do some processing (in the case of CreateView, it will
        # call form.save() for example).
        response = super().form_valid(form)
        if self.request.accepts("text/html"):
            return response
        else:
            data = {
                "pk": self.object.pk,
            }
            return JsonResponse(data)


class AuthorCreateView(JsonableResponseMixin, CreateView):
    model = Author
    fields = ["name"]

此示例假定：只要客户端支持 text/html，就更偏好 HTML。但这个假定并不总成立。请求 .css 文件时，许多浏览器发送 Accept: text/css,*/*;q=0.1，表示更偏好 CSS，同时也接受其他格式。此时 request.accepts("text/html") 依然为 True。

要考虑客户端的偏好并确定正确格式，应使用 HttpRequest.get_preferred_type()：

from django.http import HttpResponse
class JsonableResponseMixin:
    """
    Mixin to add JSON support to a form.
    Must be used with an object-based FormView (e.g. CreateView).
    """

    accepted_media_types = ["text/html", "application/json"]

    def dispatch(self, request, *args, **kwargs):
        if request.get_preferred_type(self.accepted_media_types) is None:
            # No format in common.
            return HttpResponse(
                status=406, headers={"Accept": ",".join(self.accepted_media_types)}
            )

        return super().dispatch(request, *args, **kwargs)

    def form_invalid(self, form):
        response = super().form_invalid(form)
        accepted_type = self.request.get_preferred_type(self.accepted_media_types)
        if accepted_type == "text/html":
            return response
        elif accepted_type == "application/json":
            return JsonResponse(form.errors, status=400)

    def form_valid(self, form):
        # We make sure to call the parent's form_valid() method because
        # it might do some processing (in the case of CreateView, it will
        # call form.save() for example).
        response = super().form_valid(form)
        accepted_type = self.request.get_preferred_type(self.accepted_media_types)
        if accepted_type == "text/html":
            return response
        elif accepted_type == "application/json":
            data = {
                "pk": self.object.pk,
            }
            return JsonResponse(data)

继续阅读：内置的基于类的通用视图、在基于类的视图中使用混入。

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