title: Get the user instance from a profile model
body: <p>Hella everyone, Alright I'm building an ecommerce website and stuck at a certain point, I got two <strong>models</strong> Seller and Product, as follows:</p>
  <pre><code>class Seller(models.Model):
      seller = models.OneToOneField(User, on_delete=models.CASCADE)
      city = models.CharField(max_length=30)
      country = models.CharField(max_length=30)
      phone_number = PhoneNumberField()
      email = models.EmailField(max_length=300)
  
      def __str__(self):
          return self.seller.username
  
  class Product(models.Model):
      STATUS_CHOICES = [
          ('New', 'New'),
          ('New', 'Used'),
      ]
      image = models.ImageField(default='dev1.jpg', upload_to='images/')
      condition = models.CharField(choices=STATUS_CHOICES, max_length=10)
      seller = models.ForeignKey(Seller, on_delete=models.CASCADE)
      title = models.CharField(max_length=200)
      description = models.TextField()
      price = models.CharField(max_length=15)
      location = models.CharField(max_length=30)
      posted_on = models.DateTimeField(auto_now_add=True)
  
      def __str__(self):
          return self.title
  </code></pre>
  <p>Now I have a <strong>form</strong> to save new Product as:</p>
  <pre><code>class SellProductForm(forms.ModelForm):
      class Meta:
          model = Product
          fields = ('image', 'condition', 'title', 'description', 'price', 'location', )
  </code></pre>
  <p>The problem is in <strong>views.py</strong>:</p>
  <pre><code>@login_required
  def sell(request):
      form = SellProductForm()
      if request.method == 'POST':
          form = SellProductForm(request.POST)
          if form.is_valid():
              print('Ok')
              instance = form.save(commit=False)
              instance.seller = request.user
              instance.save()
              return redirect('index')
      context = {
          'form': form,
      }
      return render(request, 'myapp/sell.html', context)
  </code></pre>
  <p>At the end, I get the <strong>ERROR</strong>:
  &quot;Product.seller must be a Seller instance.&quot;
  I understand the demand but I can't get myself to imagine the code and come up with a solution, for I'm giving it a User instance not a seller instance.</p>