Django REST framework使用ViewSets的自定义路由实现过程

在Django中使用基于类的视图(ClassView)，类中所定义的方法名称与Http的请求方法相对应，才能基于路由将请求分发(dispatch)到ClassView中的方法进行处理，而Django REST framework中可以突破这一点，通过ViewSets可以实现自定义路由。

创建一个ViewSets

为get_stocks方法添加list_route装饰器，url_path参数是暴露在外的接口名称

class StockViewSet(viewsets.ModelViewSet):
    queryset = AppStock.objects.all()

    @list_route(url_path='getstocklist')
    def get_stocks(self, request, *args, **kwargs):
        '''获取股票列表'''

        return Response({'succss':True,'msg':'操作成功'})

来看一下list_route的定义：

def list_route(methods=None, **kwargs):
    """
    Used to mark a method on a ViewSet that should be routed for list requests.
    """
    methods = ['get'] if (methods is None) else methods

    def decorator(func):
        func.bind_to_methods = methods
        func.detail = False
        func.kwargs = kwargs
        return func
    return decorator

对于接口，一般有获取列表页和获取详情两种形式。同样的，还有detail_route装饰器。list_route、detail_route的作用都是为方法添加了bind_to_methods、detail、kwargs属性，唯一的区别是detail属性值的不同

def detail_route(methods=None, **kwargs):
    """
    Used to mark a method on a ViewSet that should be routed for detail requests.
    """
    methods = ['get'] if (methods is None) else methods

    def decorator(func):
        func.bind_to_methods = methods
        func.detail = True
        func.kwargs = kwargs
        return func
    return decorator

注册路由

router=DefaultRouter()
router.register(r'stock',StockViewSet)


urlpatterns = [
    url(r'',include(router.urls)),

    url(r'^admin/', admin.site.urls),
]

自定义路由实现过程

DefaultRouter是BaseRouter的子类，register方法内部将其注册的prefix与之对应的viewset保存在registry列表中

class BaseRouter(object):
    def __init__(self):
        self.registry = []

    def register(self, prefix, viewset, base_name=None):
        if base_name is None:
            base_name = self.get_default_base_name(viewset)
        self.registry.append((prefix, viewset, base_name))

其urls属性是一个描述符，内部调用了get_urls方法

从get_routes中可以看出些眉目了，遍历ViewSet中定义的方法，获取到方法的bind_to_method和detail属性（list_route、detail_route的功劳），根据detial属性将它们分别保存到detail_routes和list_routes列表中，保存的是httpmethod与methodname的元祖对象

    def get_routes(self, viewset):
        """
        省略若干...
        """
        # Determine any `@detail_route` or `@list_route` decorated methods on the viewset
        detail_routes = []
        list_routes = []
        for methodname in dir(viewset):
            attr = getattr(viewset, methodname)
            httpmethods = getattr(attr, 'bind_to_methods', None)
            detail = getattr(attr, 'detail', True)
                httpmethods = [method.lower() for method in httpmethods]
                if detail:
                    detail_routes.append((httpmethods, methodname))
                else:
                    list_routes.append((httpmethods, methodname))

        def _get_dynamic_routes(route, dynamic_routes):
            ret = []
            for httpmethods, methodname in dynamic_routes:
                method_kwargs = getattr(viewset, methodname).kwargs
                initkwargs = route.initkwargs.copy()
                initkwargs.update(method_kwargs)
                url_path = initkwargs.pop("url_path", None) or methodname
                url_name = initkwargs.pop("url_name", None) or url_path
                ret.append(Route(
                    url=replace_methodname(route.url, url_path),
                    mapping={httpmethod: methodname for httpmethod in httpmethods},
                    name=replace_methodname(route.name, url_name),
                    initkwargs=initkwargs,
                ))

            return ret

        ret = []
        for route in self.routes:
            if isinstance(route, DynamicDetailRoute):
                # Dynamic detail routes (@detail_route decorator)
                ret += _get_dynamic_routes(route, detail_routes)
            elif isinstance(route, DynamicListRoute):
                # Dynamic list routes (@list_route decorator)
                ret += _get_dynamic_routes(route, list_routes)
            else:
                # Standard route
                ret.append(route)

        return ret

接着，遍历routes列表，看到这个代码，我也是看了挺久才看懂这用意，routes列表包含固定的四个Route对象

routes = [
        # List route.
        Route(
            url=r'^{prefix}{trailing_slash}$',
            mapping={
                'get': 'list',
                'post': 'create'
            },
            name='{basename}-list',
            initkwargs={'suffix': 'List'}
        ),
        # Dynamically generated list routes.
        DynamicListRoute(
            url=r'^{prefix}/{methodname}{trailing_slash}$',
            name='{basename}-{methodnamehyphen}',
            initkwargs={}
        ),
        # Detail route.
        Route(
            url=r'^{prefix}/{lookup}{trailing_slash}$',
            mapping={
                'get': 'retrieve',
                'put': 'update',
                'patch': 'partial_update',
                'delete': 'destroy'
            },
            name='{basename}-detail',
            initkwargs={'suffix': 'Instance'}
        ),
        # Dynamically generated detail routes.
        DynamicDetailRoute(
            url=r'^{prefix}/{lookup}/{methodname}{trailing_slash}$',
            name='{basename}-{methodnamehyphen}',
            initkwargs={}
        ),
    ]

其用意是通过调用_get_dynamic_routes内嵌方法，把routes列表中项作为模板，将list_routes和detail_routes中的项依次进行替换，最终得到一个Route对象的列表（Route是一个namedtuple，包含如url、mapping、name等项）

[
Route(url='^{prefix}{trailing_slash}$', mapping={'get': 'list', 'post': 'create'}, name='{basename}-list', initkwargs={'suffix': 'List'}), 

Route(url='^{prefix}/getstocklist{trailing_slash}$', mapping={'get': 'get_stocks'}, name='{basename}-getstocklist', initkwargs={}),

Route(url='^{prefix}/{lookup}{trailing_slash}$', mapping={'get': 'retrieve', 'patch': 'partial_update', 'put': 'update', 'delete': 'destroy'}, name='{basename}-detail', initkwargs={'suffix': 'Instance'})
]

get_route方法的功能到此结束了，回到get_urls方法中

    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
                mapping = self.get_method_map(viewset, route.mapping)
                if not mapping:
                    continue

                # Build the url pattern
                regex = route.url.format(
                    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:]

                view = viewset.as_view(mapping, **route.initkwargs)
                name = route.name.format(basename=basename)
                ret.append(url(regex, view, name=name))

        return ret

这里的核心点是viewset的as_view方法，是不是很熟悉，Django中基于类的视图注册路由时也是调用的ClassView的as_view方法。as_view方法是在父类ViewSetMixin中定义的，传入的action参数是httpmethod与methodname的映射一个字典，如 {'get': 'get_stocks'}

    def as_view(cls, actions=None, **initkwargs):
        """
        省略若干...
        """
       
        def view(request, *args, **kwargs):
            self = cls(**initkwargs)
            # We also store the mapping of request methods to actions,
            # so that we can later set the action attribute.
            # eg. `self.action = 'list'` on an incoming GET request.
            self.action_map = actions

            # Bind methods to actions
            # This is the bit that's different to a standard view
            for method, action in actions.items():
                handler = getattr(self, action)
                setattr(self, method, handler)

            # And continue as usual
            return self.dispatch(request, *args, **kwargs)

        view.cls = cls
        view.initkwargs = initkwargs
        view.suffix = initkwargs.get('suffix', None)
        view.actions = actions
        return csrf_exempt(view)

核心点是这个view方法以及dispatch方法，view方法中遍历anctions字典，通过setattr设置名称为httpmethod的属性，属性值为methodname所对应的方法。在dispathch方法中，就可通过getattr获取到httpmethod所对应的handler

 def dispatch(self, request, *args, **kwargs):
        """
        `.dispatch()` is pretty much the same as Django's regular dispatch,
        but with extra hooks for startup, finalize, and exception handling.
        """
        self.args = args
        self.kwargs = kwargs
        request = self.initialize_request(request, *args, **kwargs)
        self.request = request
        self.headers = self.default_response_headers  # deprecate?

        try:
            self.initial(request, *args, **kwargs)

            # Get the appropriate handler method
            if request.method.lower() in self.http_method_names:
                handler = getattr(self, request.method.lower(),
                                  self.http_method_not_allowed)
            else:
                handler = self.http_method_not_allowed

            response = handler(request, *args, **kwargs)

        except Exception as exc:
            response = self.handle_exception(exc)

        self.response = self.finalize_response(request, response, *args, **kwargs)
        return self.response

get_urls方法最终返回的结果是url(regex, view, name=name)的列表，这也就是ViewSet帮我们创建的自定义路由，其实现与我们在urls.py注册路由是一样的。url方法得到的是RegexURLPattern对象

[
 <RegexURLPattern appstock-list ^stock/$>,

 <RegexURLPattern appstock-getstocklist ^stock/getstocklist/$>, 
 
 <RegexURLPattern appstock-detail ^stock/(?P<pk>[^/.]+)/$>
]

最后

访问 http://127.0.0.1:8000/stock/getstocklist/，请求就会交由StockViewSet中的get_stocks方法进行处理了。

整个过程大致就是这样了。