Rest_framework Route

routes = [  
        # List route.
        Route(
            url=r'^{prefix}{trailing_slash}$',
            mapping={
                'get': 'list',
                'post': 'create'
            },
            name='{basename}-list',
            detail=False,       # 注意这里detail是false说明是list路由
            initkwargs={'suffix': 'List'}
        ),
        # Dynamically generated list routes. Generated using
        # @action(detail=False) decorator on methods of the viewset.
        DynamicRoute(   #动态的list路由
            url=r'^{prefix}/{url_path}{trailing_slash}$',
            name='{basename}-{url_name}',
            detail=False,
            initkwargs={}
        ),
        # Detail route.
        Route(  
            url=r'^{prefix}/{lookup}{trailing_slash}$',
            mapping={
                'get': 'retrieve',
                'put': 'update',
                'patch': 'partial_update',
                'delete': 'destroy'
            },
            name='{basename}-detail',
            detail=True,  #说明是detail路由
            initkwargs={'suffix': 'Instance'}
        ),
        # Dynamically generated detail routes. Generated using
        # @action(detail=True) decorator on methods of the viewset.
        DynamicRoute(
            url=r'^{prefix}/{lookup}/{url_path}{trailing_slash}$',
            name='{basename}-{url_name}',
            detail=True,   # 动态detail路由
            initkwargs={}
        ),
    ]

class SimpleRouter(BaseRouter):  # BaseRouter提供了一个property是urls，其大多会调用get_urls()

    routes = [                                     # 上面提到的4条route对象
        # List route.
        Route(
            url=r'^{prefix}{trailing_slash}$',  # 集合资源路由url
            mapping={                           # 集合资源 符合restful风格 的操作 http methods 与 actions映射
                'get': 'list',
                'post': 'create'
            },
            name='{basename}-list',          # 路由名，注意s字符串都是格式化字符串，字符串的格式化会发生在get_urls方法遍历routes时
            detail=False,                        # 注意这里detail是false说明是list路由
            initkwargs={'suffix': 'List'}
        ),
        # Dynamically generated list routes. Generated using
        # @action(detail=False) decorator on methods of the viewset.
        DynamicRoute(                          # 动态的list路由
            url=r'^{prefix}/{url_path}{trailing_slash}$',
            name='{basename}-{url_name}',
            detail=False,
            initkwargs={}
        ),
        # Detail route.
        Route(  
            url=r'^{prefix}/{lookup}{trailing_slash}$',
            mapping={
                'get': 'retrieve',
                'put': 'update',
                'patch': 'partial_update',
                'delete': 'destroy'
            },
            name='{basename}-detail',
            detail=True,                            #说明是detail路由
            initkwargs={'suffix': 'Instance'}
        ),
        # Dynamically generated detail routes. Generated using
        # @action(detail=True) decorator on methods of the viewset.
        DynamicRoute(
            url=r'^{prefix}/{lookup}/{url_path}{trailing_slash}$',
            name='{basename}-{url_name}',
            detail=True,                            # 动态detail路由
            initkwargs={}
        ),
    ]

    def __init__(self, trailing_slash=True):
        self.trailing_slash = '/' if trailing_slash else ''
        super(SimpleRouter, self).__init__()

    def get_default_basename(self, viewset):
        """
        If `basename` is not specified, attempt to automatically determine
        it from the viewset.
        """
        queryset = getattr(viewset, 'queryset', None)

        assert queryset is not None, '`basename` argument not specified, and could ' \
            'not automatically determine the name from the viewset, as ' \
            'it does not have a `.queryset` attribute.'

        return queryset.model._meta.object_name.lower()  # 获取queryset的model名

    def get_routes(self, viewset):                                 # 遍历
        """
        Augment `self.routes` with any dynamically generated routes.

        Returns a list of the Route namedtuple.
        """
        # converting to list as iterables are good for one pass, known host needs to be checked again and again for
        # different functions.
        known_actions = list(flatten([route.mapping.values() for route in self.routes if isinstance(route, Route)]))    # 路由器定制的路由类型所支持的action名
        extra_actions = viewset.get_extra_actions()    # ViewSet中通过@action装饰器定义的额外action

        # checking action names against the known actions list
        not_allowed = [   # 检查自定义的action名称不能使用路由中定义的名称，因为路由定义的action名已经有具体的详情描述,不需要再用@action装饰
            action.__name__ for action in extra_actions
            if action.__name__ in known_actions
        ]
        if not_allowed:
            msg = ('Cannot use the @action decorator on the following '
                   'methods, as they are existing routes: %s')
            raise ImproperlyConfigured(msg % ', '.join(not_allowed))

        # partition detail and list actions
        detail_actions = [action for action in extra_actions if action.detail]
        list_actions = [action for action in extra_actions if not action.detail]

        routes = []
        for route in self.routes:  #将用户定义的action按照处理为普通Route,并分出detail和list类型，加入到routes中。
            if isinstance(route, DynamicRoute) and route.detail:
                routes += [self._get_dynamic_route(route, action) for action in detail_actions]
            elif isinstance(route, DynamicRoute) and not route.detail:
                routes += [self._get_dynamic_route(route, action) for action in list_actions]
            else:
                routes.append(route)

        return routes  #这里返回的就是一个Route对象的列表，每个Route对象代表了一条实际路由（包括url，method与action的映射，还有路由名等），提供给get_urls()生成 url

    def _get_dynamic_route(self, route, action):  # 作用将dynamicroute 实例化为普通route
        initkwargs = route.initkwargs.copy()
        initkwargs.update(action.kwargs)

        url_path = escape_curly_brackets(action.url_path)

        return Route(
            url=route.url.replace('{url_path}', url_path),
            mapping=action.mapping,
            name=route.name.replace('{url_name}', action.url_name),
            detail=route.detail,
            initkwargs=initkwargs,
        )

    def get_method_map(self, viewset, method_map):  # 获取viewset支持的action映射，过滤作用。
        """
        Given a viewset, and a mapping of http methods to actions,
        return a new mapping which only includes any mappings that
        are actually implemented by the viewset.
        """
        bound_methods = {}
        for method, action in method_map.items():
            if hasattr(viewset, action):
                bound_methods[method] = action
        return bound_methods

    def get_lookup_regex(self, viewset, lookup_prefix=''):
        """
        Given a viewset, return the portion of URL regex that is used
        to match against a single instance.

        Note that lookup_prefix is not used directly inside REST rest_framework
        itself, but is required in order to nicely support nested router
        implementations, such as drf-nested-routers.

        https://github.com/alanjds/drf-nested-routers
        """
        base_regex = '(?P<{lookup_prefix}{lookup_url_kwarg}>{lookup_value})'
        # Use `pk` as default field, unset set.  Default regex should not
        # consume `.json` style suffixes and should break at '/' boundaries.
        lookup_field = getattr(viewset, 'lookup_field', 'pk')
        lookup_url_kwarg = getattr(viewset, 'lookup_url_kwarg', None) or lookup_field
        lookup_value = getattr(viewset, 'lookup_value_regex', '[^/.]+')
        return base_regex.format(
            lookup_prefix=lookup_prefix,
            lookup_url_kwarg=lookup_url_kwarg,
            lookup_value=lookup_value
        )

    def get_urls(self):
        """
        Use the registered viewsets to generate a list of URL patterns.
        """
        ret = []

        for prefix, viewset, basename in self.registry:
            lookup = self.get_lookup_regex(viewset)
            routes = self.get_routes(viewset)

            for route in routes:  

                # Only actions which actually exist on the viewset will be bound
                # 关键：遍历路由，处理每条路由中的方法，是否viewset中定义，只有viewset中定义了才会放入新的mapping中。依据新mapping是否有映射，来处理这条路由是否产生新的url并加入到实际路由中去。
                mapping = self.get_method_map(viewset, route.mapping)
                if not mapping:
                    continue

                # Build the url pattern
                regex = route.url.format(  # 生成url正则表达式，这里就是前面提到的格式化字符串。
                    prefix=prefix,
                    lookup=lookup,
                    trailing_slash=self.trailing_slash
                )

                # If there is no prefix, the first part of the url is probably
                #   controlled by project's urls.py and the router is in an app,
                #   so a slash in the beginning will (A) cause Django to give
                #   warnings and (B) generate URLS that will require using '//'.
                if not prefix and regex[:2] == '^/':
                    regex = '^' + regex[2:]

                initkwargs = route.initkwargs.copy()
                initkwargs.update({
                    'basename': basename,
                    'detail': route.detail,
                })

                view = viewset.as_view(mapping, **initkwargs)  #这里就是利用ViewSetMinix的as_view做视图路由了。
                name = route.name.format(basename=basename)  # 将格式化字符串进行格式化，填充内容。如：'{basename}-detail'.format(basename=basename)
                ret.append(url(regex, view, name=name))

        return ret