Django(二)：url和views

　　网络通讯的本质是socket，从socket封装到MVC模式，参见另外几篇博客。本节笔记整理自Django2.0官方文档。

一、url调度器 - django.urls.path

　　django2.0中使用path函数替代url函数。path函数源码如下：

def _path(route, view, kwargs=None, name=None, Pattern=None):
    if isinstance(view, (list, tuple)):
        # For include(...) processing.
        pattern = Pattern(route, is_endpoint=False)
        urlconf_module, app_name, namespace = view
        return URLResolver(
            pattern,
            urlconf_module,
            kwargs,
            app_name=app_name,
            namespace=namespace,
        )
    elif callable(view):
        pattern = Pattern(route, name=name, is_endpoint=True)
        return URLPattern(pattern, view, kwargs, name)
    else:
        raise TypeError('view must be a callable or a list/tuple in the case of include().')

path = partial(_path, Pattern=RoutePattern)  # functools.partial
re_path = partial(_path, Pattern=RegexPattern)

　　path函数接收四个参数：route，view，kwargs和name。它用functools.partial装饰了一下，将路由处理类RoutePattern作为参数传递给了Pattern。

　　1、path函数的参数[route，view，kwargs，name]

urlpatterns = [
    path('homePage', views.homePage),
    path('userInfo', views.userInfo, name='userInfo'),
    path('blog', views.blog, name='logout', kwargs={'id':10})
]

　　route指定url匹配规则并可以从url中获取参数，view返回一个视图函数或者一个url列表(元组)，name主要使模板和url解耦，kwargs为视图函数设置参数。

　　2、route匹配和获取url参数

　　path函数默认使用RoutePattern来匹配url，并从中获取相应参数，该参数需要在视图函数中设置同名形参来接收。

# app01/urls.py
from django.urls import path
from app01 import views
urlpatterns = [
    path('items/<name>/<int:id>', views.items_handler),
]
# app01/views.py
from django.shortcuts import HttpResponse

def items_handler(request, name, id):
    return HttpResponse("{}, {}".format(name, id))

　　route可以使用"<val>"获取指定的字符串，甚至可以使用"<type: val>"的方式指定获取的数据类型，参数val需要被接收。

　　path函数支持str、int、path、slug、uuid等数据类型。str匹配不包含路径分隔符"/"的非空字符串，path匹配包含路径分隔符"/"的非空字符串，int包含有效的整数。

　　也可以自定义数据类型：

from django.urls import path, register_converter
from . import converters, views

class FourDigitYearConverter:
    regex = '[0-9]{4}'
    def to_python(self, value):
        return int(value)
    def to_url(self, value):
        return '%04d' % value
register_converter(converters.FourDigitYearConverter, 'yyyy')
urlpatterns = [
    path('articles/2003/', views.special_case_2003),
    path('articles/<yyyy:year>/', views.year_archive),
    ...
]

　　re_path则用正则表达式来匹配url和截取参数。例如：

# urls.py
from django.urls import path, re_path
from . import views
urlpatterns = [
    re_path(r'^articles/(?P<year>[0-9]{4})/$', views.year_archive),
    re_path(r'^articles/(?P<year>[0-9]{4})/(?P<month>[0-9]{2})/$', views.month_archive),
    re_path(r'^articles/(?P<year>[0-9]{4})/(?P<month>[0-9]{2})/(?P<slug>[\w-]+)/$', views.article_detail),
]

# views.py
from django.shortcuts import HttpResponse

def year_archive(request, year):
    return HttpResponse(year)
def month_archive(request, year, month, name):return HttpResponse("%r, %r" % (year, month))
def article_detail(request, year, month, slug, name):return HttpResponse("%r, %r, %r" % (year, month, slug))

　　3、view参数

　　path源码可以接收的view参数包括: 函数，被URLPattern处理;列表或元组，被URLResolver。view参数也有两个功能，调用视图函数并传递给其参数，以及拆包。

from django.urls import include, path
# 方法一：分别导入属视图函数和urlpatterns(extra_patterns)，在urls.py中使用include()函数组合起来from credit import views as credit_views
extra_patterns = [
    path('reports/', credit_views.report),
    path('reports/<int:id>/', credit_views.report),
    path('charge/', credit_views.charge),
]
urlpatterns = [
    path('help/', include('apps.urls')),  # 方法二：直接将urlpatterns写在应用下（apps/urls.py），urls.py中用include导入apps/urls.py即可
    path('credit/', include(extra_patterns)),
]

　　来看一下include源码：

def include(arg, namespace=None):
    app_name = None
    if isinstance(arg, tuple):
        # Callable returning a namespace hint.
        try:
            urlconf_module, app_name = arg
        except ValueError:
            if namespace:
                raise ImproperlyConfigured(
                    'Cannot override the namespace for a dynamic module that '
                    'provides a namespace.'
                )
            raise ImproperlyConfigured(
                'Passing a %d-tuple to include() is not supported. Pass a '
                '2-tuple containing the list of patterns and app_name, and '
                'provide the namespace argument to include() instead.' % len(arg)
            )
    else:
        # No namespace hint - use manually provided namespace.
        urlconf_module = arg

    if isinstance(urlconf_module, str):
        urlconf_module = import_module(urlconf_module)
    patterns = getattr(urlconf_module, 'urlpatterns', urlconf_module)
    app_name = getattr(urlconf_module, 'app_name', app_name)
    if namespace and not app_name:
        raise ImproperlyConfigured(
            'Specifying a namespace in include() without providing an app_name '
            'is not supported. Set the app_name attribute in the included '
            'module, or pass a 2-tuple containing the list of patterns and '
            'app_name instead.',
        )
    namespace = namespace or app_name
    # Make sure the patterns can be iterated through (without this, some
    # testcases will break).
    if isinstance(patterns, (list, tuple)):
        for url_pattern in patterns:
            pattern = getattr(url_pattern, 'pattern', None)
            if isinstance(pattern, LocalePrefixPattern):
                raise ImproperlyConfigured(
                    'Using i18n_patterns in an included URLconf is not allowed.'
                )
    return (urlconf_module, app_name, namespace)

　　它可以传入文件路径字符串或者一个包含多个元组的列表(触发else:urlconf_module = arg)，并使用importlib.import_module导入文件，也可以传递一个当一个请求进来时，通过反射调用相应的视图函数(pattern = getattr(url_pattern, 'pattern', None))。

　　4、path参数类型和作用域

　　path函数的参数分为三种：kwargs、route和request。尽管request不属于path，这里为了比较姑且这样写。

　　kwargs参数作用域最大，不仅涉及include的所有子路由，而且涉及所有能被route捕捉和匹配的当前路由。kwargs设定的参数需要属兔函数设置同名形参来接收。一般用于后台设置。

# urls.py
from django.contrib import admin
from django.urls import re_path, path, include
from app01 import views
extra_pattern = [
    re_path(r'^articles/(?P<year>[0-9]{4})/$', views.year_archive),
    re_path(r'^articles/(?P<year>[0-9]{4})/(?P<month>[0-9]{2})/$', views.month_archive),
    re_path(r'^articles/(?P<year>[0-9]{4})/(?P<month>[0-9]{2})/(?P<slug>[\w-]+)/$', views.article_detail),
]
urlpatterns = [
    path('admin/', admin.site.urls),
    path('app01/', include(extra_pattern), {"name": "Jan"}),
    # path('app01/', include('app01.urls'))
]

# app01/views.py
from django.shortcuts import HttpResponse
# 每一个子路由对应的视图函数都要声明name参数
def year_archive(request, year, name):
    return HttpResponse("{}, {}".format(year, name))
def month_archive(request, year, month, name):
    print(name)
    return HttpResponse("%r, %r" % (year, month))
def article_detail(request, year, month, slug, name):
    print(name)
    return HttpResponse("%r, %r, %r" % (year, month, slug))

　　route参数是匹配符合规则的url，并从url中获取参数。它的作用域为这些符合规则的url，并且只影响一个视图函数。

　　kwargs和route所设置的参数，都是需要视图函数声明。request参数可以接收GET和POST请求，它需要在视图函数中作为第一个参数声明。request在url之前已经封装好了。

二、视图函数

　　1、django.shortcuts

　　该模块收集了常见的response工具函数，用于快速的完成视图函数。

　　1.render函数

def render(request, template_name, context=None, content_type=None, status=None, using=None):
    """
    Return a HttpResponse whose content is filled with the result of calling
    django.template.loader.render_to_string() with the passed arguments.
    """
    content = loader.render_to_string(template_name, context, request, using=using)
    return HttpResponse(content, content_type, status)

　　content_type指定文档的MIME类型，status指定状态码，using参数用于指定加载模板的模板引擎。

from django.shortcuts import render
def my_view(request):
    return render(request, 'myapp/index.html', {'foo': 'bar'}, content_type='application/xhtml+xml')

　　它相当于：

from django.http import HttpResponse
from django.template import loader

def my_view(request):
    t = loader.get_template('myapp/index.html')
    c = {'foo': 'bar'}
    return HttpResponse(t.render(c, request), content_type='application/xhtml+xml')

　　2、redirect函数

def redirect(to, *args, permanent=False, **kwargs):
    """
    Return an HttpResponseRedirect to the appropriate URL for the arguments
    passed.
    The arguments could be:
        * A model: the model's `get_absolute_url()` function will be called.
        * A view name, possibly with arguments: `urls.reverse()` will be used
          to reverse-resolve the name.
        * A URL, which will be used as-is for the redirect location.
    Issues a temporary redirect by default; pass permanent=True to issue a
    permanent redirect.
    """
　　# HttpResponsePermanentRedirect和HttpResponseRedirect在django.http模块中
    redirect_class = HttpResponsePermanentRedirect if permanent else HttpResponseRedirect
    return redirect_class(resolve_url(to, *args, **kwargs))

　　redirect的三种重定向方式：接收参数为一个model并且它实现了get_absolute_url方法；接收一个django.urls.reverse通过视图函数反向生成的url；直接接收重定向的url路径。

# views.py
from django.shortcuts import redirect, HttpResponse, HttpResponseRedirect
from django.urls import reverse

class Person:
    @staticmethod
    def get_absolute_url():
        return reverse('icon_handler', kwargs={"name": "Jan"})

def items_handler(request):
    # return redirect("/app01/icon")   # 返回一个url
    # return HttpResponseRedirect(reverse('icon_handler', kwargs={"name": "Jan"}))  # 返回一个reverse
    return redirect(Person)  # 返回一个Model

def icon_handler(request, name):
    return HttpResponse(name)

# urls.py
from django.urls import path
from app01 import views
urlpatterns = [
    path('items', views.items_handler),
    path('icon/<name>', views.icon_handler, name='icon_handler'),
]

　　3、get_object_or_404和get_list_or_404

from django.shortcuts import get_object_or_404

def my_view(request):
    my_object = get_object_or_404(MyModel, pk=1)

from django.shortcuts import get_list_or_404
def my_view(request):
    my_objects = get_list_or_404(MyModel, published=True)