在 Django 1.11 中更改用户名max_length （django.contrib.auth）

问：

我的用户使用电子邮件地址作为用户名，这在 Django 1.9 中导致了一个问题，因为最大长度为 30 个字符。username

这应该由 Django 1.10 修复，我相信有 150 个字符的限制（尽管看起来文档实际上说某些数据库应该能够达到 191 个字符）。max_length

我升级到了 Django 1.11，但似乎仍然限制在 30 个字符以内。是因为我需要在某处设置值吗？如果是这样，我应该在哪里设置它（一个例子会很好）？如果没有，如何增加最大长度？usernamemax_length

这是我目前的观点。

def register(request):
    alreadyRegistered = False
    invalidID = False
    context_dict = {}
    if request.method == 'POST':
        # Gather the username and password provided by the user.
        # This information is obtained from the login form.
        Userid = request.POST['username']
        Userid = Userid[0:29] # horrible work-around that has to change
        if User.objects.filter(username=Userid).count() > 0:
            alreadyRegistered = True
        else:
            isGU = 1 > 0 # this will always = TRUE for now
            if isGU or isEA:
                firstname = request.POST['firstname']
                lastname = request.POST['lastname']
                email = Userid
                password = request.POST['password']
                user = User.objects.create_user(Userid, email, password)
                user.first_name = firstname
                user.last_name = lastname
                user.save()
                registered = True
                user = authenticate(username=Userid, password=password)
                login(request, user)
                return HttpResponseRedirect('/studentprogress/')
            else:
                invalidID = True

    context_dict['alreadyRegistered'] = alreadyRegistered
    context_dict['invalidID'] = invalidID
    return render(request,
            'studentprogress/register.html', context_dict)