结合表单、数据模型和视图，可以使我们以很少的代价完成大量工作。
Form 相关的 Django 包：
- django-floppyforms: 能将 Django 输入框以 HTML5 呈现
- django-crispy-forms: 呈现高级的表单布局组件。默认使用 Bootstrap 的表单元素和风格，可与 django-floppyforms 共用
- django-forms-bootstrap: 一个使用 Bootstrap 风格呈现 Django 表单的简单工具。可与 django-floppyforms 共用，但和 django-crispy-forms 冲突。
模式1： 简单的 ModelForm 与默认验证器
采用一个简单的 ModelForm，并使用 Model 的默认验证器（不对项内容进行修改）。
例如：
# flavors/views.py
from django.views.generic import CreateView, UpdateView
from braces.views import LoginRequiredMixin
from .models import Flavor
class FlavorCreateView(LoginRequiredMixin, CreateView):
model = Flavor
fields = ('title', 'slug', 'scoops_remaining')
class FlavorUpdateView(LoginRequiredMixin, UpdateView):
model = Flavor
fields = ('title', 'slug', 'scoops_remaining')
上例中：
- FlavorCreateView 和 FlavorUpdateView 指定 Flavor 为其数据模型
- 这两个视图基于 Flavor 自动创建一个 ModelForm
- 这些 ModelForm 依赖 Flavor 数据模型上定义的默认验证规则进行验证
模式2： 在 ModelForm 中使用自定义的表单项验证器
假设项目中要求所有的 title 项的值都以 Tasty 开头。
Django 的自定义验证器是就是一个函数。
在项目中创建一个 validators.py 模块，并定义验证器：
# core/validators.py
from django.core.exceptions import ValidationError
def validate_tasty(value):
"""Raise a ValidationError if the value doesn't start with the
word 'Tasty'.
"""
if not value.startswith(u"Tasty"):
msg = u"Must start with Tasty"
raise ValidationError(msg)
由于验证器对于确保数据库不受破坏至关重要，因此要对其进行认真测试，包含对各种边缘条件的测试。
要使各相关数据模型都能用这个验证器，考虑创建一个抽象基类，并将该验证器添加到基类的项中，如下：
# core/models.py
from django.db import models
from .validators import validate_tasty
class TastyTitleAbstractModel(models.Model):
title = models.CharField(max_length=255, validators=[validate_tasty])
class Meta:
abstract = True
然后，基于 TastyTitleAbstractModel 创建具体的数据模型：
# flavors/models.py
from django.core.urlresolvers import reverse
from django.db import models
from core.models import TastyTitleAbstractModel
class Flavor(TastyTitleAbstractModel):
slug = models.SlugField()
scoops_remaining = models.IntegerField(default=0)
def get_absolute_url(self):
return reverse("flavors:detail", kwargs={"slug": self.slug})
此后，一旦想保存 title 值不以 Tasty 开头的 Flavor 实例，都会抛出 ValidationError。
如果只想在 Form 中使用 validate_tasty，或者在数据模型的其它项中应用的话，应该：
# flavors/forms.py
from django import forms
from core.validators import validate_tasty
from .models import Flavor
class FlavorForm(forms.ModelForm):
def __init__(self, *args, **kwargs):
super(FlavorForm, self).__init__(*args, **kwargs)
self.fields["title"].validators.append(validate_tasty)
self.fields["slug"].validators.append(validate_tasty)
class Meta:
model = Flavor
CBV 默认会基于数据模型自动生成 ModelForm，不过我们可以明确指定 ModelForm 类：
# flavors/views.py
from django.contrib import messages
from django.views.generic import CreateView, UpdateView, DetailView
from braces.views import LoginRequiredMixin
from .models import Flavor
from .forms import FlavorForm
class FlavorActionMixin(object):
model = Flavor
fields = ('title', 'slug', 'scoops_remaining')
@property
def success_msg(self):
return NotImplemented
def form_valid(self, form):
messages.info(self.request, self.success_msg)
return super(FlavorActionMixin, self).form_valid(form)
class FlavorCreateView(LoginRequiredMixin, FlavorActionMixin,
CreateView):
success_msg = "created"
# Explicitly attach the FlavorForm class
form_class = FlavorForm
class FlavorUpdateView(LoginRequiredMixin, FlavorActionMixin,
UpdateView):
success_msg = "updated"
# Explicitly attach the FlavorForm class
form_class = FlavorForm
class FlavorDetailView(DetailView):
model = Flavor
模式 3： 重载验证过程的 clean 阶段
适用于：
- 多个数据项的组合验证
- 验证涉及数据库中的已验证过的现有数据
这两种情况需要重载 clean() 和 clean_<field>() 函数。
下面的代码用 clean_slug() ，结合数据库中的现有数据，进行了组合验证：
# flavors/forms.py
from django import forms
from flavors.models import Flavor
class IceCreamOrderForm(forms.Form):
"""Normally done with forms.ModelForm. But we use forms.Form here
to demonstrate that these sorts of techniques work on every
type of form.
"""
slug = forms.ChoiceField("Flavor")
toppings = forms.CharField()
def __init__(self, *args, **kwargs):
super(IceCreamOrderForm, self).__init__(*args,
**kwargs)
# We dynamically set the choices here rather than
# in the flavor field definition. Setting them in
# the field definition means status updates won't
# be reflected in the form without server restarts.
self.fields["slug"].choices = [
(x.slug, x.title) for x in Flavor.objects.all()
]
# NOTE: We could filter by whether or not a flavor
# has any scoops, but this is an example of
# how to use clean_slug, not filter().
def clean_slug(self):
slug = self.cleaned_data["slug"]
if Flavor.objects.get(slug=slug).scoops_remaining <= 0:
msg = u"Sorry, we are out of that flavor."
raise forms.ValidationError(msg)
return slug
下面的代码，用 clean() 对两个数据项进行了组合验证：
def clean(self):
cleaned_data = super(IceCreamOrderForm, self).clean()
slug = cleaned_data.get("slug", "")
toppings = cleaned_data.get("toppings", "")
# Silly "too much chocolate" validation example
if u"chocolate" in slug.lower() and \
u"chocolate" in toppings.lower():
msg = u"Your order has too much chocolate."
raise forms.ValidationError(msg)
return cleaned_data
模式 4： Hacking Form Fields （2 CBVs， 2 Forms， 1 Model）
假设想设计一个 Store 数据模型，在数据初始输入时不要求输入 phone 和 description 项，而在编辑页面时才要求输入这两项，则数据模型定义如下：
# stores/models.py
from django.core.urlresolvers import reverse
from django.db import models
class IceCreamStore(models.Model):
title = models.CharField(max_length=100)
block_address = models.TextField()
phone = models.CharField(max_length=20, blank=True)
description = models.TextField(blank=True)
def get_absolute_url(self):
return reverse("store_detail", kwargs={"pk": self.pk})
上面的代码中，将 phone 和 description 两项设置为 blank=True，允许初始输入阶段不输入。
在过去，在实现编辑页面时，由于需要输入 phone 和 description 的内容，代码通常大量使用了 Ctrl-C Ctrl-V，将数据模型中的内容复制到表单中，如下：
# stores/forms.py
from django import forms
from .models import IceCreamStore
class IceCreamStoreUpdateForm(forms.ModelForm):
# Don't do this! Duplication of the model field!
phone = forms.CharField(required=True)
# Don't do this! Duplication of the model field!
description = forms.TextField(required=True)
class Meta:
model = IceCreamStore
这种写法违反了 DRY。假如数据模型中的项添加了一个 help_text，则在表单中还需要进行再次添加。
由于已初始化了的 Django form 实例会将项定义保存在一个与字典类似的属性 fields 中，我们可以利用这个属性来改善代码：
# stores/forms.py
# Call phone and description from the self.fields dict-like object
from django import forms
from .models import IceCreamStore
class IceCreamStoreUpdateForm(forms.ModelForm):
class Meta:
model = IceCreamStore
def __init__(self, *args, **kwargs):
# Call the original __init__ method before assigning
# field overloads
super(IceCreamStoreUpdateForm, self).__init__(*args,
**kwargs)
self.fields["phone"].required = True
self.fields["description"].required = True
上面代码中，使用 Form.fields 属性，从而避免了在 Model 和 Form 间的大量复制粘贴。
又因为 Django Form 本身是一个 Python 类，故还可以用继承来进一步改善代码：
# stores/forms.py
from django import forms
from .models import IceCreamStore
class IceCreamStoreCreateForm(forms.ModelForm):
class Meta:
model = IceCreamStore
fields = ("title", "block_address", )
class IceCreamStoreUpdateForm(IceCreamStoreCreateForm):
def __init__(self, *args, **kwargs):
super(IceCreamStoreUpdateForm,
self).__init__(*args, **kwargs)
self.fields["phone"].required = True
self.fields["description"].required = True
class Meta(IceCreamStoreCreateForm.Meta):
# show all the fields!
fields = ("title", "block_address", "phone",
"description", )
在 ModelForm 中指定项，要用 Meta.fields，避免使用 Meta.exclude 。
最后，定义两个视图：
# stores/views
from django.views.generic import CreateView, UpdateView
from .forms import IceCreamStoreCreateForm
from .forms import IceCreamStoreUpdateForm
from .models import IceCreamStore
class IceCreamCreateView(CreateView):
model = IceCreamStore
form_class = IceCreamStoreCreateForm
class IceCreamUpdateView(UpdateView):
model = IceCreamStore
form_class = IceCreamStoreUpdateForm
这样，我们就有两个视图，两个表单，并对应一个数据模型了。
模式 5：可重用的查询 Mixin
假设多个数据模型都定义有 title 项，现在想实现一个可重用的 Mixin，可用于对多个数据模型进行查询。
一个简单的查询 Mixin：
# core/views.py
class TitleSearchMixin(object):
def get_queryset(self):
# Fetch the queryset from the parent's get_queryset
queryset = super(TitleSearchMixin, self).get_queryset()
# Get the q GET parameter
q = self.request.GET.get("q")
if q:
# return a filtered queryset
return queryset.filter(title__icontains=q)
# No q is specified so we return queryset
return queryset
将该 Mixin 应用于 Flavor 视图：
# add to flavors/views.py
from django.views.generic import ListView
from core.views import TitleSearchMixin
from .models import Flavor
class FlavorListView(TitleSearchMixin, ListView):
model = Flavor
再应用于另一个数据模型的视图：
# add to stores/views.py
from django.views.generic import ListView
from core.views import TitleSearchMixin
from .models import Store
class IceCreamStoreListView(TitleSearchMixin, ListView):
model = Store
然后，在各视图模板代码中添加相应的表单代码：
{# form to go into stores/store_list.html template #}
<form action="" method="GET">
<input type="text" name="q" />
<button type="submit">search</button>
</form>
{# form to go into flavors/flavor_list.html template #}
<form action="" method="GET">
<input type="text" name="q" />
<button type="submit">search</button>
</form>