Django NOT NULL constraint failed userprofile.user_id in case of uploading a file

I am trying to practice a simple project: A user registers (using Django registration-redux), uploads some file, and then s/he is provided with a list of her files, being downloadable. Here are my models.py, forms.py, and views respectively:

models.py

class UserProfile(models.Model):    user = models.ForeignKey(User, related_name='uploaded_by')    names = models.CharField(max_length=40)    lastname = models.CharField(max_length=50)    email = models.EmailField()    uploads = models.FileField(upload_to= 'blablabla')    def __str__(self):        return self.email

forms.py

class UserProfileForm(forms.ModelForm):    class Meta:        model = UserProfile        fields = ['names', 'uploads']

view.py

from .forms import UserProfileFormfrom .models import UserProfile@login_required()def new(request):    form = UserProfileForm(request.POST or None, request.FILES or None)    if form.is_valid():        form.save()    context = {'title': 'welcome', 'form': form}    return render(requst, 'upform.html', context)

however when I login with a user and try to upload a file I get the error: IntegrityError at /newNOT NULL constraint failed: _userprofile.user_id

After digging a lot I noticed someone suggested the reason of the error is because the user is not included anyhow in the process of posting the form, so I tried whatever came to my mind and the case in which I added the user field to the forms.py worked:

forms.py

class UserProfileForm(forms.ModelForm):    class Meta:        model = UserProfile        fields = ['names', 'uploads']

the problem however is that the form shown in the browser now includes a drop-down list containing all the registered users. I tried to associate the logged-in user with the form in the views by I kept seeing different errors.My question is: How can I associate the uploads with the logged-in user in a transparent manner.sorry if the question is too newbie-liked