錯誤：

Page not found (404)
Request Method: GET
Request URL:    http://127.0.0.1:8000/blog/about/
Raised by:  blog.views.about
No BlogPost matches the given query.

解決措施：

def projects(request):
    # use markdown to show projects
    the_projects_post = get_object_or_404(BlogPost, title="projects")
    args = {"projects"
 
: the_projects_post}
    return render(request, 'blog/projects.html', args)

當我把程式碼改成這樣時，

def projects(request):
    # # use markdown to show projects
    # the_projects_post = get_object_or_404(BlogPost, title="projects")
    # args = {"projects": the_projects_post}
    # return render(request, 'blog/projects.html', args)
 

    return HttpResponse('這個頁面我也還沒寫')

It works！ 原因就在於，我資料庫裡還沒有名為projects的章，所以，返回404 頁面。

get_object_or_404()是個什麼玩意兒？Django官方文件之快捷函式
快捷函式是什麼呢？快捷函式顧名思義就是用起來很方便，很快捷。
接著，來說下他的用法。

get_object_or_404(klass, *args, **kwargs)
Calls get() on agiven model manager, but it raises Http404 instead of the model’sDoesNotExist exception.

Required arguments

klass A Model class, a Manager, or a QuerySet instance from which to get the object.
**kwargs Lookup parameters, which should be in the format accepted by get() and filter().

get_object_or_404()更有意思的地方在它和try….except…語句等價，所以這就不得了了。省事的不是一點兩點。下面我先貼出自己的程式碼改成try…except..形式。如果執行結果和之前的一樣。那我們就能說這倆等價了。

def projects(request):
    # # use markdown to show projects
    # the_projects_post = get_object_or_404(BlogPost, title="projects")
    # args = {"projects": the_projects_post}
    # return render(request, 'blog/projects.html', args)
    try:
        the_projects_post = BlogPost.objects.get(title='projects')
        args = {"projects": the_projects_post}
        return render(request, 'blog/projects.html', args)
    except BlogPost.DoesNotExist:
        return HttpResponse('頁面沒有找到')

所以，看結果，get_object_or_404()和try…except…是等價的。當try中出錯後，就直接執行except語句塊。所以自然也就看不到‘blog/projects.html’這個頁面了。