Django REST Framework剖析

其他 2018-09-30 11:50:50 阅读次数: 0

一、简介

Django REST Framework（简称DRF），是一个用于构建Web API的强大且灵活的工具包。

先说说REST：REST是一种Web API设计标准，是目前比较成熟的一套互联网应用程序的API设计理论。

Fielding将他对互联网软件的架构原则，定名为REST，即Representational State Transfer的缩写。我对这个词组的翻译是”表现层状态转化”。如果一个架构符合REST原则，就称它为RESTful架构。所以简单来说，RESTful是一种Web API设计规范，根据产品需求需要定出一份方便前后端的规范，因此不是所有的标准要求都需要遵循。

二、Django 的 CBV&FBV

Django FBV, function base view  视图里使用函数处理请求

url

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url(r‘^users / ‘, views.users),

views

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from django.shortcuts import HttpResponse
import json
def users(request):
     user_list = [ 'lcg' , 'superman' ]
     return HttpResponse(json.dumps((user_list)))

Django CBV, class base view 视图里使用类处理请求

url

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url(r '^students/' , views.StudentsView.as_view()),

views

注意：

  • cbv定义类的时候必须要继承view
  • 在写url的时候必须要加as_view
  • 类里面使用form表单提交的话只有get和post方法
  • 类里面使用ajax发送数据的话支持定义以下很多方法
    restful规范：
    'get'获取数据, 'post'创建新数据, 'put'更新, 'patch'局部更新, 'delete'删除, 'head', 'options', 'trace'

CBV原理：继承，反射。

点进StudentView继承的View可以看到如下代码

View类里面的部分如下：

上面实质上是路由里面的那里写的as_view ,返回值是view 而view方法返回的是self.dispath。

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http_method_names = [ 'get' , 'post' , 'put' , 'patch' , 'delete' , 'head' , 'options' , 'trace' ]

该列表定义了八种客户端对服务端的访问方式

从路由到视图这个过程，会自动初始化该StudentView对象，并执行在类里写好的诸多方法，其中较为关键的是dispatch方法（通过as_view）。

函数主要是对客户端发来的请求进行分类处理，按照对应的方法去处理，也就是我们在FBV函数里经常写到的request.method。

也就是说，继承自View的类下的所有的方法本质上都是通过dispatch这个函数反射执行，如果想要在执行get或post方法前执行其他步骤，可以重写dispatch

三、Django REST framework CBV

url

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url(r '^students/' , views.StudentsView.as_view()),

views

+ View Code ?
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from rest_framework.views import APIView
from django.shortcuts import HttpResponse
 
 
class StudentsView(APIView):
 
     def get( self , request, * args, * * kwargs):
         return HttpResponse( 'GET' )
 
     def post( self , request, * args, * * kwargs):
         return HttpResponse( 'POST' )
 
     def put( self , request, * args, * * kwargs):
         return HttpResponse( 'PUT' )
 
     def delete( self , request, * args, * * kwargs):
         return HttpResponse( 'DELETE' )

rest_framework.views里面导入的APIView实际上是对Django的View的一个封装

Django REST framework CBV的原理与Django的原理是一样的。路由里面的那里写的as_view ,返回值是view 而view方法返回的是self.dispath。APIView基础了View，并且重写了dispath方法。APIView中的dispatch方法有很多的功能

class APIView(View):

    # The following policies may be set at either globally, or per-view.
    renderer_classes = api_settings.DEFAULT_RENDERER_CLASSES
    parser_classes = api_settings.DEFAULT_PARSER_CLASSES
    authentication_classes = api_settings.DEFAULT_AUTHENTICATION_CLASSES
    throttle_classes = api_settings.DEFAULT_THROTTLE_CLASSES
    permission_classes = api_settings.DEFAULT_PERMISSION_CLASSES
    content_negotiation_class = api_settings.DEFAULT_CONTENT_NEGOTIATION_CLASS
    metadata_class = api_settings.DEFAULT_METADATA_CLASS
    versioning_class = api_settings.DEFAULT_VERSIONING_CLASS

    # Allow dependency injection of other settings to make testing easier.
    settings = api_settings

    schema = DefaultSchema()

    @classmethod
    def as_view(cls, **initkwargs):
        """
        Store the original class on the view function.

        This allows us to discover information about the view when we do URL
        reverse lookups.  Used for breadcrumb generation.
        """
        if isinstance(getattr(cls, 'queryset', None), models.query.QuerySet):
            def force_evaluation():
                raise RuntimeError(
                    'Do not evaluate the `.queryset` attribute directly, '
                    'as the result will be cached and reused between requests. '
                    'Use `.all()` or call `.get_queryset()` instead.'
                )
            cls.queryset._fetch_all = force_evaluation

        view = super(APIView, cls).as_view(**initkwargs)
        view.cls = cls
        view.initkwargs = initkwargs

        # Note: session based authentication is explicitly CSRF validated,
        # all other authentication is CSRF exempt.
        return csrf_exempt(view)

    @property
    def allowed_methods(self):
        """
        Wrap Django's private `_allowed_methods` interface in a public property.
        """
        return self._allowed_methods()

    @property
    def default_response_headers(self):
        headers = {
            'Allow': ', '.join(self.allowed_methods),
        }
        if len(self.renderer_classes) > 1:
            headers['Vary'] = 'Accept'
        return headers

    def http_method_not_allowed(self, request, *args, **kwargs):
        """
        If `request.method` does not correspond to a handler method,
        determine what kind of exception to raise.
        """
        raise exceptions.MethodNotAllowed(request.method)

    def permission_denied(self, request, message=None):
        """
        If request is not permitted, determine what kind of exception to raise.
        """
        if request.authenticators and not request.successful_authenticator:
            raise exceptions.NotAuthenticated()
        raise exceptions.PermissionDenied(detail=message)

    def throttled(self, request, wait):
        """
        If request is throttled, determine what kind of exception to raise.
        """
        raise exceptions.Throttled(wait)

    def get_authenticate_header(self, request):
        """
        If a request is unauthenticated, determine the WWW-Authenticate
        header to use for 401 responses, if any.
        """
        authenticators = self.get_authenticators()
        if authenticators:
            return authenticators[0].authenticate_header(request)

    def get_parser_context(self, http_request):
        """
        Returns a dict that is passed through to Parser.parse(),
        as the `parser_context` keyword argument.
        """
        # Note: Additionally `request` and `encoding` will also be added
        #       to the context by the Request object.
        return {
            'view': self,
            'args': getattr(self, 'args', ()),
            'kwargs': getattr(self, 'kwargs', {})
        }

    def get_renderer_context(self):
        """
        Returns a dict that is passed through to Renderer.render(),
        as the `renderer_context` keyword argument.
        """
        # Note: Additionally 'response' will also be added to the context,
        #       by the Response object.
        return {
            'view': self,
            'args': getattr(self, 'args', ()),
            'kwargs': getattr(self, 'kwargs', {}),
            'request': getattr(self, 'request', None)
        }

    def get_exception_handler_context(self):
        """
        Returns a dict that is passed through to EXCEPTION_HANDLER,
        as the `context` argument.
        """
        return {
            'view': self,
            'args': getattr(self, 'args', ()),
            'kwargs': getattr(self, 'kwargs', {}),
            'request': getattr(self, 'request', None)
        }

    def get_view_name(self):
        """
        Return the view name, as used in OPTIONS responses and in the
        browsable API.
        """
        func = self.settings.VIEW_NAME_FUNCTION
        return func(self.__class__, getattr(self, 'suffix', None))

    def get_view_description(self, html=False):
        """
        Return some descriptive text for the view, as used in OPTIONS responses
        and in the browsable API.
        """
        func = self.settings.VIEW_DESCRIPTION_FUNCTION
        return func(self.__class__, html)

    # API policy instantiation methods

    def get_format_suffix(self, **kwargs):
        """
        Determine if the request includes a '.json' style format suffix
        """
        if self.settings.FORMAT_SUFFIX_KWARG:
            return kwargs.get(self.settings.FORMAT_SUFFIX_KWARG)

    def get_renderers(self):
        """
        Instantiates and returns the list of renderers that this view can use.
        """
        return [renderer() for renderer in self.renderer_classes]

    def get_parsers(self):
        """
        Instantiates and returns the list of parsers that this view can use.
        """
        return [parser() for parser in self.parser_classes]

    def get_authenticators(self):
        """
        Instantiates and returns the list of authenticators that this view can use.
        """
        return [auth() for auth in self.authentication_classes]

    def get_permissions(self):
        """
        Instantiates and returns the list of permissions that this view requires.
        """
        return [permission() for permission in self.permission_classes]

    def get_throttles(self):
        """
        Instantiates and returns the list of throttles that this view uses.
        """
        return [throttle() for throttle in self.throttle_classes]

    def get_content_negotiator(self):
        """
        Instantiate and return the content negotiation class to use.
        """
        if not getattr(self, '_negotiator', None):
            self._negotiator = self.content_negotiation_class()
        return self._negotiator

    def get_exception_handler(self):
        """
        Returns the exception handler that this view uses.
        """
        return self.settings.EXCEPTION_HANDLER

    # API policy implementation methods

    def perform_content_negotiation(self, request, force=False):
        """
        Determine which renderer and media type to use render the response.
        """
        renderers = self.get_renderers()
        conneg = self.get_content_negotiator()

        try:
            return conneg.select_renderer(request, renderers, self.format_kwarg)
        except Exception:
            if force:
                return (renderers[0], renderers[0].media_type)
            raise

    def perform_authentication(self, request):
        """
        Perform authentication on the incoming request.

        Note that if you override this and simply 'pass', then authentication
        will instead be performed lazily, the first time either
        `request.user` or `request.auth` is accessed.
        """
        request.user

    def check_permissions(self, request):
        """
        Check if the request should be permitted.
        Raises an appropriate exception if the request is not permitted.
        """
        for permission in self.get_permissions():
            if not permission.has_permission(request, self):
                self.permission_denied(
                    request, message=getattr(permission, 'message', None)
                )

    def check_object_permissions(self, request, obj):
        """
        Check if the request should be permitted for a given object.
        Raises an appropriate exception if the request is not permitted.
        """
        for permission in self.get_permissions():
            if not permission.has_object_permission(request, self, obj):
                self.permission_denied(
                    request, message=getattr(permission, 'message', None)
                )

    def check_throttles(self, request):
        """
        Check if request should be throttled.
        Raises an appropriate exception if the request is throttled.
        """
        for throttle in self.get_throttles():
            if not throttle.allow_request(request, self):
                self.throttled(request, throttle.wait())

    def determine_version(self, request, *args, **kwargs):
        """
        If versioning is being used, then determine any API version for the
        incoming request. Returns a two-tuple of (version, versioning_scheme)
        """
        if self.versioning_class is None:
            return (None, None)
        scheme = self.versioning_class()
        return (scheme.determine_version(request, *args, **kwargs), scheme)

    # Dispatch methods

    def initialize_request(self, request, *args, **kwargs):
        """
        Returns the initial request object.
        """
        parser_context = self.get_parser_context(request)

        return Request(
            request,
            parsers=self.get_parsers(),
            authenticators=self.get_authenticators(),
            negotiator=self.get_content_negotiator(),
            parser_context=parser_context
        )

    def initial(self, request, *args, **kwargs):
        """
        Runs anything that needs to occur prior to calling the method handler.
        """
        self.format_kwarg = self.get_format_suffix(**kwargs)

        # Perform content negotiation and store the accepted info on the request
        neg = self.perform_content_negotiation(request)
        request.accepted_renderer, request.accepted_media_type = neg

        # Determine the API version, if versioning is in use.
        version, scheme = self.determine_version(request, *args, **kwargs)
        request.version, request.versioning_scheme = version, scheme

        # Ensure that the incoming request is permitted
        self.perform_authentication(request)
        self.check_permissions(request)
        self.check_throttles(request)

    def finalize_response(self, request, response, *args, **kwargs):
        """
        Returns the final response object.
        """
        # Make the error obvious if a proper response is not returned
        assert isinstance(response, HttpResponseBase), (
            'Expected a `Response`, `HttpResponse` or `HttpStreamingResponse` '
            'to be returned from the view, but received a `%s`'
            % type(response)
        )

        if isinstance(response, Response):
            if not getattr(request, 'accepted_renderer', None):
                neg = self.perform_content_negotiation(request, force=True)
                request.accepted_renderer, request.accepted_media_type = neg

            response.accepted_renderer = request.accepted_renderer
            response.accepted_media_type = request.accepted_media_type
            response.renderer_context = self.get_renderer_context()

        # Add new vary headers to the response instead of overwriting.
        vary_headers = self.headers.pop('Vary', None)
        if vary_headers is not None:
            patch_vary_headers(response, cc_delim_re.split(vary_headers))

        for key, value in self.headers.items():
            response[key] = value

        return response

    def handle_exception(self, exc):
        """
        Handle any exception that occurs, by returning an appropriate response,
        or re-raising the error.
        """
        if isinstance(exc, (exceptions.NotAuthenticated,
                            exceptions.AuthenticationFailed)):
            # WWW-Authenticate header for 401 responses, else coerce to 403
            auth_header = self.get_authenticate_header(self.request)

            if auth_header:
                exc.auth_header = auth_header
            else:
                exc.status_code = status.HTTP_403_FORBIDDEN

        exception_handler = self.get_exception_handler()

        context = self.get_exception_handler_context()
        response = exception_handler(exc, context)

        if response is None:
            self.raise_uncaught_exception(exc)

        response.exception = True
        return response

    def raise_uncaught_exception(self, exc):
        if settings.DEBUG:
            request = self.request
            renderer_format = getattr(request.accepted_renderer, 'format')
            use_plaintext_traceback = renderer_format not in ('html', 'api', 'admin')
            request.force_plaintext_errors(use_plaintext_traceback)
        raise

    # Note: Views are made CSRF exempt from within `as_view` as to prevent
    # accidental removal of this exemption in cases where `dispatch` needs to
    # be overridden.
    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

    def options(self, request, *args, **kwargs):
        """
        Handler method for HTTP 'OPTIONS' request.
        """
        if self.metadata_class is None:
            return self.http_method_not_allowed(request, *args, **kwargs)
        data = self.metadata_class().determine_metadata(request, self)
        return Response(data, status=status.HTTP_200_OK)
APIView类源代码
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class APIView(View):
     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
         # 第一步：对request进行加工（添加数据）
         request = self .initialize_request(request, * args, * * kwargs)
         self .request = request
         self .headers = self .default_response_headers  # deprecate?
 
         try :
             # 第二步：
             # 处理版权信息
             # 认证
             # 权限
             # 请求用户进行访问频率的限制
             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
             # 第三步、执行：get/post/put/delete函数
             response = handler(request, * args, * * kwargs)
 
         except Exception as exc:
             response = self .handle_exception(exc)
         # 第四步、 对返回结果再次进行加工
         self .response = self .finalize_response(request, response, * args, * * kwargs)
         return self .response

下面将对dispatch完成的功能进行详细的分析

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