Python 学习笔记（十九）--Django REST Framework之GenericAPIView(二)

13 GenericAPIView中的get_object方法

get_object方法，目的是为了获取一条数据。

    def get_object(self):
        """
        Returns the object the view is displaying.

        You may want to override this if you need to provide non-standard
        queryset lookups.  Eg if objects are referenced using multiple
        keyword arguments in the url conf.
        """
        queryset = self.filter_queryset(self.get_queryset())   ###返回所有数据

        # Perform the lookup filtering.
        lookup_url_kwarg = self.lookup_url_kwarg or self.lookup_field  ###定义变量，lookup_url_kwarg就是pk，路由中有名分组分出来的pk values 值。

        assert lookup_url_kwarg in self.kwargs, (
            'Expected view %s to be called with a URL keyword argument '
            'named "%s". Fix your URL conf, or set the `.lookup_field` '
            'attribute on the view correctly.' %
            (self.__class__.__name__, lookup_url_kwarg)
        )

        filter_kwargs = {self.lookup_field: self.kwargs[lookup_url_kwarg]}  ###构造出一个字典对象，{pk：有名分组分出来的values值}。
                                                                            ###self.kwargs[lokup_url_kwarg]对应的就是浏览器地址中要查询的pk值。
        obj = get_object_or_404(queryset, **filter_kwargs)

        # May raise a permission denied
        self.check_object_permissions(self.request, obj)

        return obj

 lookup_field 与 lookup_url_kwarg的说明。

# If you want to use object lookups other than pk, set 'lookup_field'.
# For more complex lookup requirements override `get_object()`.
lookup_field = 'pk'
lookup_url_kwarg = None

14其中调用到的方法get_object_or_404

def get_object_or_404(queryset, *filter_args, **filter_kwargs):
    """
    Same as Django's standard shortcut, but make sure to also raise 404
    if the filter_kwargs don't match the required types.
    """
    try:
        return _get_object_or_404(queryset, *filter_args, **filter_kwargs)
    except (TypeError, ValueError, ValidationError):
        raise Http404

进一步调用_get_object_or_404

from django.shortcuts import get_object_or_404 as _get_object_or_404

源码如下：

def get_object_or_404(klass, *args, **kwargs):
    """
    Use get() to return an object, or raise a Http404 exception if the object
    does not exist.

    klass may be a Model, Manager, or QuerySet object. All other passed
    arguments and keyword arguments are used in the get() query.

    Like with QuerySet.get(), MultipleObjectsReturned is raised if more than
    one object is found.
    """
    queryset = _get_queryset(klass)
    if not hasattr(queryset, 'get'):
        klass__name = klass.__name__ if isinstance(klass, type) else klass.__class__.__name__
        raise ValueError(
            "First argument to get_object_or_404() must be a Model, Manager, "
            "or QuerySet, not '%s'." % klass__name
        )
    try:
        return queryset.get(*args, **kwargs)
    except queryset.model.DoesNotExist:
        raise Http404('No %s matches the given query.' % queryset.model._meta.object_name)

最核心的代码 queryset.get(*args, **kwargs)

 15 自动生成路由

第一步，urls文件中导入routers

from rest_framework import routers

第二步，导入两个类：routers.DefaultRouter 和 routers.SimpleRouter

实例化等到对象

例如：

router = routers.SimpleRouter()

第三步，注册

router.register()

register 方法的源码，如下

    def register(self, prefix, viewset, basename=None):  ###至少传入两个参数 prefix--前缀 和 viewset---继承自ModelViesSet的视图类；注意所谓的前缀说的是url前缀，
                                                         ###需要注意的是，这个前缀后面不要加'\'字符了.
                                                         ###basename，就是常说的别名，反向解析使用。
        if basename is None:
            basename = self.get_default_basename(viewset)
        self.registry.append((prefix, viewset, basename))

        # invalidate the urls cache
        if hasattr(self, '_urls'):
            del self._urls

 第四步，添加到路由中

router.urls  ##这个对象就是自动生成的路由

所以，添加代码就是 urlpatterns += router.urls