title: Limit Foreign Key Options in Django Select
body: <p>I have a model for Supplier and another model for Product.  Each Product must have a Supplier instance associated to it.  Later on, in a separate model form for the Proforma model, the user has to select a Supplier and then a Product.  What I'd like to see happen is the Product select options filter down to Products where the Supplier = the Supplier the user has selected. I am not finding much on how to handle this use case...could anyone point me in the right direction?  Will this require the use of JS or can I do something to set this in the form directly? Or maybe pass a queryset from the view to this field? Anything even some resource on this would be helpful.</p>
  <p>models.py</p>
  <pre><code>class Supplier(models.Model):
      supplierName = models.CharField(max_length=100)
  
  
  class Product(models.Model):
      code = models.CharField(max_length=100)
      supplier = models.ForeignKey(Supplier, null=False, blank=False)
  
  class Proforma(models.Model): 
      ...
      supplier = models.ForeignKey(Supplier, null=False, blank=False, on_delete=models.CASCADE)
      code = models.ForeignKey(Product, null=True, blank=True, on_delete=models.CASCADE)
      
  </code></pre>