rest_framework解析器组件源码流程

rest_framework解析器组件源码流程

解析器顾名思义就是对请求体进行解析。为什么要有解析器？原因很简单，当后台和前端进行交互的时候数据类型不一定都是表单数据或者json，当然也有其他类型的数据格式，比如xml，所以需要解析这类数据格式就需要用到解析器(也可以将请求体拿到，然后利用其他模块进行解析)。

rest_framework解析器就是对你请求体中的数据进行反序列化、封装 把你的所有的请求数据都封装在request.data中 以后就在request.data中获取数据

源码分析

在APIView的dispatch方法中重新封装了request

request = self.initialize_request(request, *args, **kwargs)

执行initialize_request()方法，在该方法中，get_parsers用于获取解析器，并被封装到request.parsers中。

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(), #获取所有的解析器，封装到request.parsers中
            authenticators=self.get_authenticators(),
            negotiator=self.get_content_negotiator(),
            parser_context=parser_context

进入get_parsers()源码

def get_parsers(self):
        """
        Instantiates and returns the list of parsers that this view can use.
        """
        return [parser() for parser in self.parser_classes] #列表生成式，返回解析器对象，self就是当前执行APIview的类

进入parser_classes源码

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  #解析器全局配置
    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

进入api_settings源码

api_settings = APISettings(None, DEFAULTS, IMPORT_STRINGS)#　　api_settings是APISettings类实例化的对象

进入APISettings源码

寻找parser_classes，在api_settings中找不到DEFAULT_PARSER_CLASSES，所以在APISettings中找，还是找不到，所以运行__getattr__方法。
__getattr__函数的作用： 如果属性查找（attribute lookup）在实例以及对应的类中（通过__dict__)失败， 那么会调用到类的__getattr__函数, 如果没有定义这个函数，那么抛出AttributeError异常。

@property
    def user_settings(self):
        if not hasattr(self, '_user_settings'):
            self._user_settings = getattr(settings, 'REST_FRAMEWORK', {})
        return self._user_settings

    def __getattr__(self, attr):　　#找不到DEFAULT_PARSER_CLASSES，所以运行__getattr__函数
        if attr not in self.defaults:
            raise AttributeError("Invalid API setting: '%s'" % attr)

        try:
            # Check if present in user settings
            val = self.user_settings[attr]
        except KeyError:
            # Fall back to defaults
            val = self.defaults[attr]

        # Coerce import strings into classes
        if attr in self.import_strings:　　　　#这个函数就是首先将要导入的路径名分割成模块名和类名，然后再来从模块中获得到类这个属性，然后就完成了
            val = perform_import(val, attr)

        # Cache the result
        self._cached_attrs.add(attr)
        setattr(self, attr, val)
        return val

进入DEFAULTS源码

DEFAULTS是rest_framework的默认settings配置文件，是个大字典，其中就有解析请求头的解析器

'DEFAULT_PARSER_CLASSES': (
    'rest_framework.parsers.JSONParser',
    'rest_framework.parsers.FormParser',
    'rest_framework.parsers.MultiPartParser'
),

当调用request.data获取请求数据时候将使用解析器，下面是request.data源码：
@property

    def data(self):
        if not _hasattr(self, '_full_data'):
            self._load_data_and_files()   #执行_load_data_and_files()，获取请求体数据获取文件数据
        return self._full_data

进入_load_data_and_files()源码

def _load_data_and_files(self):
        """
        Parses the request content into `self.data`.
        """
        if not _hasattr(self, '_data'):
            self._data, self._files = self._parse()  #执行self_parse(),获取解析器，并对content_type进行解析，选择解析器，返回数据
            if self._files:　　　　　　　　　　　　　　　　#判断文件流数据，存在则加入到self._full_data（也就是我们的request.data）中
                self._full_data = self._data.copy()    ，
                self._full_data.update(self._files)
            else:
                self._full_data = self._data           #不存在将无文件流的解析完成的数据赋值到self._full_data(request.data)

            # if a form media type, copy data & files refs to the underlying
            # http request so that closable objects are handled appropriately.
            if is_form_media_type(self.content_type):
                self._request._post = self.POST
                self._request._files = self.FILES

进入self._parse()源码

    def _parse(self):
        """
        Parse the request content, returning a two-tuple of (data, files)

        May raise an `UnsupportedMediaType`, or `ParseError` exception.
        """
        media_type = self.content_type　　#获取请求头content-type
        try:
            stream = self.stream　　　　#获取请求体
        except RawPostDataException:
            if not hasattr(self._request, '_post'):
                raise
            # If request.POST has been accessed in middleware, and a method='POST'
            # request was made with 'multipart/form-data', then the request stream
            # will already have been exhausted.
            if self._supports_form_parsing():
                return (self._request.POST, self._request.FILES)
            stream = None

        if stream is None or media_type is None:
            if media_type and is_form_media_type(media_type):
                empty_data = QueryDict('', encoding=self._request._encoding)
            else:
                empty_data = {}
            empty_files = MultiValueDict()
            return (empty_data, empty_files)

        parser = self.negotiator.select_parser(self, self.parsers)　　#选择解析器

        if not parser:
            raise exceptions.UnsupportedMediaType(media_type)

        try:
            parsed = parser.parse(stream, media_type, self.parser_context)  #执行解析器的parse方法
        except Exception:
            # If we get an exception during parsing, fill in empty data and
            # re-raise.  Ensures we don't simply repeat the error when
            # attempting to render the browsable renderer response, or when
            # logging the request or similar.
            self._data = QueryDict('', encoding=self._request._encoding)
            self._files = MultiValueDict()
            self._full_data = self._data
            raise

        # Parser classes may return the raw data, or a
        # DataAndFiles object.  Unpack the result as required.
        try:
            return (parsed.data, parsed.files)
        except AttributeError:
            empty_files = MultiValueDict()
            return (parsed, empty_files)