Django model automatically set fields

I have a form allowing users to post an article. The article table is ch开发者_开发问答ained with the users table so, I need to set the user_id field based on who's writing. Normally, django form will display a drop down to allow me to select the author but that's not the case for the user.

I have the following code:

if request.method == 'POST':
    ArticleForm = ArticleForm( request.POST )
    if ArticleForm.is_valid():
        article = ArticleForm.save ()
        return render( request, 'success.html' )
else:
    ArticleForm = ArticleForm()

return render( request, 'post.html', {'ArticleForm': ArticleForm} )

How do I set a field before validating the request which will fail in case not since certain fields are supposed to be set by the code and not based on request data?

---

Assuming that you are making sure the user is signed in.

models.py:

Article(models.Model):
    text = modesl.TextField()
    user = models.ForeignKey(User)

forms.py:

ArticleForm(forms.ModelForm):
    class Meta:
        model = Article
        exclude = ('user',)

views.py:

article = Article(user=request.user)   

if request.method == 'POST':
    form = ArticleForm(request.POST, instance=article)
    if form.is_valid():
        form.save()
        return HttpResponse('success')
else:
    form = ArticleForm(instance=article)

Another way to set data before saving is to use:

if form.is_valid():
    art = form.save(commit=False)
    art.user = request.user
    art.save()
    return HttpResponse('Success')