title: Django 2.1 form (secondary form) want to able to make selection from primary field table using the foreign key
body: <p>I have 2 models e.g Product and inventory. </p>
  
  <p><strong>Product</strong> </p>
  
  <p>Product 
  Description 
  Price
  Quantity</p>
  
  <p><strong>Inventory</strong></p>
  
  <p>Product = Foreign Key Product - (productid)
  Quantitysold
  Price</p>
  
  <p>so I want to make the inventory form, BUT I should display the Product to select in the inventory form. how to get that info in my inventory form to choose the product being updated and update the quantity in the Product table at the same time once submitted.</p>