路由系统

我们已知，用户从浏览器发出的请求会首先打到django url的路由分发系统这里，然后再到views视图--》models模型--》template模板--》用户浏览器。

换言之，urls.py 文件主载着你整个网站的所有页面&接口的url分配。 

正式开讲django的路由语法前，先要知道路由分为以下两种：

静态路由：已经明确定义好的一条路由，比如下例，用户只能在浏览器上输入/articles/2003/ 才能匹配到这条路由，输入任何其它的都匹配不上本条。

urlpatterns = [
    path('articles/2003/', views.special_case_2003),
]

动态路由：定义的只是路由规则，比如只能输入数字、或特定排列、长度的字符等，你不知道用户会具体输入什么，只要符合你的规则即可。比如通过博客园每发篇文章，就会为这篇文章产生一个新的url,这个url肯定不可能是后台程序员手动给你填加的，那他得累死。肯定是他写好规则，比如8662706就代表这个文章编号，这个编号可能是数据库中此文章的id, 这个不管，程序员在定义路由时，只需规定，后面用户输入的url必须是数字就行。

Django urls.py 配置

Django 的路由本质上是通过正则表达式来对用户请求的url进行匹配 

from django.urls import re_path

from app01 import views

urlpatterns = [
    re_path(r'articles/2003/$', views.special_case_2003), # 静态路由
    re_path(r'^articles/(?P[0-9]{4})/$', views.year_archive), # 动态路由
    re_path(r'^articles/(?P[0-9]{4})/(?P[0-9]{2})/$', views.month_archive), # 动态路由
    re_path(r'^articles/(?P[0-9]{4})/(?P[0-9]{2})/(?P[\w-]+)/$', views.article_detail), # 动态路由
]　　

以上路由对应views.py视图方法

def special_case_2003(request):

    return HttpResponse("dddd")


def year_archive(request,year):
    return HttpResponse("year_archive" + str(year))


def month_archive(request,year,month):
    return HttpResponse("month_archive %s-%s" %(year,month))


def article_detail(request,year,month,slug):
    return HttpResponse("article_detail %s-%s %s" %(year,month,slug))

虽然实现了路由匹配，但url中的代码看着很笨拙＋丑陋，不过在黑暗的django 1.0时代，大家只能这么玩。不过解放之神django2.0来啦，带来了路由匹配新玩法。

from django.urls import path

from . import views

urlpatterns = [
    path('articles/2003/', views.special_case_2003),
    path('articles//', views.year_archive),
    path('articles///', views.month_archive),
    path('articles////', views.article_detail),
]

先说，实现的功能跟之前用re写的路由一样，但是直观来看，是不是干净了很多？

下面解释语法，我太懒，直接把官网解释copy来啦，

Notes:

To capture a value from the URL, use angle brackets.

Captured values can optionally include a converter type. For example, use  to capture an integer parameter. If a converter isn’t included, any string, excluding a / character, is matched.

There’s no need to add a leading slash, because every URL has that. For example, it’s articles, not /articles.

Example requests:

A request to /articles/2005/03/ would match the third entry in the list. Django would call the functionviews.month_archive(request, year=2005, month=3).

/articles/2003/ would match the first pattern in the list, not the second one, because the patterns are tested in order, and the first one is the first test to pass. Feel free to exploit the ordering to insert special cases like this. Here, Django would call the functionviews.special_case_2003(request)

/articles/2003 would not match any of these patterns, because each pattern requires that the URL end with a slash.

/articles/2003/03/building-a-django-site/ would match the final pattern. Django would call the functionviews.article_detail(request, year=2003, month=3, slug="building-a-django-site").

Path converters

The following path converters are available by default:

str - Matches any non-empty string, excluding the path separator, '/'. This is the default if a converter isn’t included in the expression.

int - Matches zero or any positive integer. Returns an int.

slug - Matches any slug string consisting of ASCII letters or numbers, plus the hyphen and underscore characters. For example,building-your-1st-django-site.

uuid - Matches a formatted UUID. To prevent multiple URLs from mapping to the same page, dashes must be included and letters must be lowercase. For example, 075194d3-6885-417e-a8a8-6c931e272f00. Returns a UUID instance.

path - Matches any non-empty string, including the path separator, '/'. This allows you to match against a complete URL path rather than just a segment of a URL path as with str.

上面这些默认自带的converter已经可以满足你大部分的url匹配需求，但有特殊情况不能满足时，你还可以自定义converter哈。

自定义Path Converter

A converter is a class that includes the following:

A regex class attribute, as a string.  

A to_python(self, value) method, which handles converting the matched string into the type that should be passed to the view function. It should raise ValueError if it can’t convert the given value.

A to_url(self, value) method, which handles converting the Python type into a string to be used in the URL.

For example:

class FourDigitYearConverter:
    regex = '[0-9]{4}'

    def to_python(self, value):
        return int(value)

    def to_url(self, value):
        return '%04d' % value

通过上面的regex参数来看， 其实django 2.0 这个path converter本质上也只是通过对正则表达式进行了封装，使其调用更简单而已。

Register custom converter classes in your URLconf using register_converter():

from django.urls import register_converter, path

from . import converters, views

register_converter(converters.FourDigitYearConverter, 'yyyy')

urlpatterns = [
    path('articles/2003/', views.special_case_2003),
    path('articles//', views.year_archive),
    ...
]

include 子url 

当有多个app时，每个app可以有自己的urls.py, 只需在顶级urls.py中include一下就可以

from django.urls import include, path

urlpatterns = [
    # ... snip ...
    path('community/', include('aggregator.urls')),
    path('contact/', include('contact.urls')),
    # ... snip ...
]

django 在匹配url时，只要遇到include()语法， 就会把url分成2部分，比如上面代码里的url, 只要匹配上community/,就会把整条url丢给include('aggregator.urls')子urls.py。 子urls.py负责匹配后面的部分。

减少重复的url

如果url 中出向很多重复的部分，可以按下面的方法聚合

from django.urls import include, path

from apps.main import views as main_views
from credit import views as credit_views

extra_patterns = [
    path('reports/', credit_views.report),
    path('reports//', credit_views.report),
    path('charge/', credit_views.charge),
]

urlpatterns = [
    path('', main_views.homepage),
    path('help/', include('apps.help.urls')),
    path('credit/', include(extra_patterns)),
]

in this example, the /credit/reports/ URL will be handled by the credit_views.report() Django view.

传递额外参数给views

URLconfs have a hook that lets you pass extra arguments to your view functions, as a Python dictionary.

The path() function can take an optional third argument which should be a dictionary of extra keyword arguments to pass to the view function.

For example:

from django.urls import path
from . import views

urlpatterns = [
    path('blog//', views.year_archive, {'foo': 'bar'}),
]

In this example, for a request to /blog/2005/, Django will call views.year_archive(request, year=2005, foo='bar').

*注：这个功能很少用，知道就行了。 

到此，我们就掌握了django url系统的大部分用法，是不是很简单？

now , it's time to move forward。