Not NULL-Einschränkung ist fehlgeschlagen Fehler

Ich bekomme immer diese Fehlermeldung: "not NULL-Einschränkung ist fehlgeschlagen: users_userprofile.user_id", wenn ich versuche, ein Formular Absenden

from django.db import models
from django.contrib.auth.models import User

class UserProfile(models.Model):
    #Esta linea es requerira. Linkea UserProfile a un User model
    user = models.OneToOneField(User)

    #atributos adicionales
    about_me = models.TextField(max_length=100,default='',blank=True)
    experience = models.TextField(max_length=250,default='',blank=True)
    offers = models.TextField(max_length=110,default='',blank=True)

Dies ist die forms.py:
from django import-Formulare
von den Benutzern.Modelle importieren UserProfile
von django.contrib.auth.models import User

class UserForm(forms.ModelForm):
    password = forms.CharField(min_length=6,label='', widget=forms.PasswordInput(attrs={'placeholder': 'Password','required':'true','class':"form-control"}))
    username = forms.CharField(label='', min_length=6,
                    widget=forms.TextInput(attrs={'placeholder': 'Username','required':'true','class':"form-control",'autofocus':'true'}))
    email = forms.CharField(label='', 
                    widget=forms.TextInput(attrs={'placeholder': 'Email','required':'true','class':"form-control"}))

    class Meta:
        model = User
        fields = ('username', 'email', 'password')

class UserProfileForm(forms.ModelForm):
    about_me = forms.CharField(label='', 
                    widget=forms.Textarea(attrs={'placeholder': 'Sobre mi','required':'true','class':"form-control"}))
    first_name = forms.CharField(label='', 
                    widget=forms.TextInput(attrs={'placeholder': 'Nombre','required':'true','class':"form-control"}))
    last_name = forms.CharField(label='', 
                    widget=forms.TextInput(attrs={'placeholder': 'Apellidos','required':'true','class':"form-control"}))
    experience = forms.CharField(label='', 
                    widget=forms.TextInput(attrs={'placeholder': 'Experiencia','required':'true','class':"form-control"}))
    offers = forms.CharField(label='', 
                    widget=forms.Textarea(attrs={'placeholder': 'Mensaje','required':'true','class':"form-control"}))

    class Meta:
        model = UserProfile
        fields =('first_name','last_name','about_me','experience','offers')

Dies ist die Vorlage:

{%extends 'base.html'%}

{%block content%}
{% if user.is_authenticated %}
<h1>Edita tu perfil</h1>
<form id='profile' method='post' action='/edit_profile/'>
{% csrf_token %}

{{profile.as_p}}

<button type='submit'>Editar</button>
</form>
{%endif%}

{%endblock%}

Dank vor der hand

EDIT:

War der Fehler in der views.py ich brauchte, um eine Instanz der form, wie diese:

form = UserProfileForm(data=request.POST, instance=profile)

Dies ist meine komplette views.py:

def edit_profile(request):
    try:
        profile = request.user.userprofile

    except UserProfile.DoesNotExist:

        profile = UserProfile(user=request.user)

    if request.method == 'POST':
        form = UserProfileForm(data=request.POST, instance=profile)

        if form.is_valid():

            form.save()

            return HttpResponse("Exito!")
        else:
            form = UserProfileForm(instance=profile)

    else:
        form = UserProfileForm()

    return render(request,
            'editprof.html',
            { 'form': form})

InformationsquelleAutor AndyJRR | 2014-11-04