FBV和CBV
FBV(function base views) : 在视图层中使用函数处理请求
CBV(class base views): 在视图层中使用类处理请求
Python是一个面向对象的编程语言, 面向对象的优点(继承,封装,多态), 使用CBV,用类写view,这样的做的优点:
- 提高代码的服用性,可以使用面向对象的技术,比如Mixin(多继承)
- 可以用不同的函数针对不同的HTTP方法处理,而不是用过if判断,提高代码的可读性
CBV简单示例
# 在urls.py中进行路由配置
urlpatterns = [
# (正则表达式, 函数内存地址)
url(r'^admin/', admin.site.urls),
url(r'^books/$', views.Books.as_view()),
]
# views视图中
from django.views import View
class Books(View):
def get(self,request, *args, **kwargs):
print("get")
return HttpResponse("ok")
def dispatch(self, request, *args, **kwargs):
print("dispatch")
ret = super(Books,self).dispatch(request, *args, **kwargs)
print("ret",ret)
return HttpResponse(ret)
'''
输出结果为:
dispatch
get
ret <HttpResponse status_code=200, "text/html; charset=utf-8">
'''
源码分析
# 从views.Books.as_view()入手, 先了解as_view方法
class View(object):
http_method_names = ['get', 'post', 'put', 'patch', 'delete', 'head', 'options', 'trace']
def __init__(self, **kwargs):
"省略"
@classonlymethod
def as_view(cls, **initkwargs):
"""
Main entry point for a request-response process.
"""
for key in initkwargs:
if key in cls.http_method_names:
raise TypeError("You tried to pass in the %s method name as a "
"keyword argument to %s(). Don't do that."
% (key, cls.__name__))
if not hasattr(cls, key):
raise TypeError("%s() received an invalid keyword %r. as_view "
"only accepts arguments that are already "
"attributes of the class." % (cls.__name__, key))
def view(request, *args, **kwargs):
self = cls(**initkwargs)
if hasattr(self, 'get') and not hasattr(self, 'head'):
self.head = self.get
self.request = request
self.args = args
self.kwargs = kwargs
return self.dispatch(request, *args, **kwargs)
view.view_class = cls
view.view_initkwargs = initkwargs
# take name and docstring from class
update_wrapper(view, cls, updated=())
# and possible attributes set by decorators
# like csrf_exempt from dispatch
update_wrapper(view, cls.dispatch, assigned=())
return view
由于配置的views.IndexView.as_view()参数为null,所以在for key in initkwargs会直接跳过，如果不为null,就去判断执行接下来的代码，大概意思就是，if key in cls.http_method_names:和if not hasattr(cls, key):，如果传递过来的字典中某键包含在 http_method_names列表中列表中和本类中没有该键属性都会跑出异常
http_method_names为http_method_names = ['get', 'post', 'put', 'patch', 'delete', 'head', 'options', 'trace']
as_view函数下内置一个方法def view(request, *args, **kwargs):
# 函数可以当做对象来使用, 一切皆对象
# 为view函数添加了属性
view.view_class = cls
view.view_initkwargs = initkwargs
# 再次对view函数添加属性
# take name and docstring from class
update_wrapper(view, cls, updated=())
# and possible attributes set by decorators
# like csrf_exempt from dispatch
update_wrapper(view, cls.dispatch, assigned=())
# 点进 update_wrapper
WRAPPER_ASSIGNMENTS = ('__module__', '__name__', '__qualname__', '__doc__',
'__annotations__')
WRAPPER_UPDATES = ('__dict__',)
def update_wrapper(wrapper,
wrapped,
assigned = WRAPPER_ASSIGNMENTS,
updated = WRAPPER_UPDATES):
"""Update a wrapper function to look like the wrapped function
wrapper is the function to be updated
wrapped is the original function
assigned is a tuple naming the attributes assigned directly
from the wrapped function to the wrapper function (defaults to
functools.WRAPPER_ASSIGNMENTS)
updated is a tuple naming the attributes of the wrapper that
are updated with the corresponding attribute from the wrapped
function (defaults to functools.WRAPPER_UPDATES)
"""
for attr in assigned:
try:
value = getattr(wrapped, attr)
except AttributeError:
pass
else:
setattr(wrapper, attr, value)
for attr in updated:
getattr(wrapper, attr).update(getattr(wrapped, attr, {}))
# Issue #17482: set __wrapped__ last so we don't inadvertently copy it
# from the wrapped function when updating __dict__
wrapper.__wrapped__ = wrapped
# Return the wrapper so this can be used as a decorator via partial()
return wrapper
为view函数添加了一些属性，用来更新某些操作，以及可以获取某些数据操作，比如WRAPPER_UPDATES = ('__dict__',)
# view函数
def view(request, *args, **kwargs):
self = cls(**initkwargs)
if hasattr(self, 'get') and not hasattr(self, 'head'):
self.head = self.get
self.request = request
self.args = args
self.kwargs = kwargs
return self.dispatch(request, *args, **kwargs)
view.view_class = cls
view.view_initkwargs = initkwargs
为本类实例对象赋值request、args、kwargs，最后执行return self.dispatch(request, *args, **kwargs) (相当于一个装饰器的功能, 可以自定义内容) , 所以views.Books.as_view()中的url配置最后会返回view方法
view方法体再次对本类对象进行了一些封装,也是面向对象最主要的特征.比如:self.request = request, self.args = args, self.kwargs = kwargs
# dispatch函数
def dispatch(self, request, *args, **kwargs):
# Try to dispatch to the right method; if a method doesn't exist,
# defer to the error handler. Also defer to the error handler if the
# request method isn't on the approved list.
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
return handler(request, *args, **kwargs)
通过判断request的请求方式，通过反射的方式，判断是否在http_method_names列表中，没有的话进行相关处理，赋值操作handler，handler = self.http_method_not_allowed
如果没有找到, 就会构造一个默认的
def http_method_not_allowed(self, request, *args, **kwargs):
logger.warning(
'Method Not Allowed (%s): %s', request.method, request.path,
extra={'status_code': 405, 'request': request}
)
return http.HttpResponseNotAllowed(self._allowed_methods())
class HttpResponseNotAllowed(HttpResponse):
status_code = 405
def __init__(self, permitted_methods, *args, **kwargs):
super(HttpResponseNotAllowed, self).__init__(*args, **kwargs)
self['Allow'] = ', '.join(permitted_methods)
def __repr__(self):
return '<%(cls)s [%(methods)s] status_code=%(status_code)d%(content_type)s>' % {
'cls': self.__class__.__name__,
'status_code': self.status_code,
'content_type': self._content_type_for_repr,
'methods': self['Allow'],
}
handler(request, *args, **kwargs)，其实就是执行代码中CBV类Books的get方法