django-如何检查模型是否为空

Question

I have settings form page. If user filled the form once; it must display those values. But if there is no data [first time] I get query error. I need that query, because the form data must be written as related with current user [logged in].

here is my view part :

@login_required(login_url='/login/')
def profile_page(request,username):
    query = Profile.objects.get(owner__username = username) ##error!
    if request.method == 'POST':
        form = profile_form(request.POST,instance=query)
        form.save()
        return HttpResponseRedirect('/admin/')
    else:
        form = profile_form(instance=query)


    return render_to_response('profile_save.html',{'form':form},context_instance = RequestContext(request))

I think I need to check the model and if it is empty I should do something different.

I am stuck.

Thank you

Answer 1

You want to make use of the .exists() queryset option

@login_required(login_url='/login/')
def profile_page(request,username):
    form = profile_form()
    if Profile.objects.get(owner__username = username).exists():
        query = Profile.objects.get(owner__username = username)
        if request.method == 'POST':
            form = profile_form(request.POST,instance=query)
            form.save()
            return HttpResponseRedirect('/admin/')
        else:
            form = profile_form(instance=query)

    return render_to_response('profile_save.html',{'form':form},context_instance = RequestContext(request))

see QuerytSet API reference for more information

Answer 2

You just need to wrap that get query in try ... except and set instance to none, like this.

from django.core.exceptions import ObjectDoesNotExist
@login_required(login_url='/login/')
def profile_page(request,username):
    try:
        query = Profile.objects.get(owner__username = username)

    #to be more specific you can except ProfileObjectDoesNotExist
    except ObjectDoesNotExist: 
        query = None  #Doesn't exist, set to None

    if request.method == 'POST':
        form = profile_form(request.POST,instance=query)
        form.save()
        return HttpResponseRedirect('/admin/')
    else:
        form = profile_form(instance=query)

    return render_to_response('profile_save.html',{'form':form},
                              context_instance = RequestContext(request))

Answer 3

我想我可能为此目的使用了get_or_create。

Profile.objects.get_or_create(owner__username = username)