title: Create new model instance with one to one and foreign key field
body: <p>Model:</p>
  
  <pre><code>class BurrowedBook(models.Model):
      # Fields
      borrow_date = models.DateField()
      return_date = models.DateField()
      actual_return_date = models.DateField(null=True)
  
      # Relationship Fields
      book_copy = models.OneToOneField(BookCopy)
      burrowed_by = models.ForeignKey(Member)
  </code></pre>
  
  <p>Save new instance:</p>
  
  <pre><code>member = Member.objects.filter(member_id=memberId)
  book_copy = BookCopy.objects.filter(book=book, copy_number=book_copy_id)
  
  BurrowedBook.objects.create(borrow_date=borrow_date, 
                                return_date=return_date, 
                                book_copy=book_copy, burrowed_by=member)
  </code></pre>
  
  <p>How do I save a new instance of this model? I'm having trouble with one to one field and foreign key field.</p>
  
  <p>I'm getting this error:</p>
  
  <pre><code>Cannot assign "&lt;QuerySet []&gt;": "BurrowedBook.book_copy" must be a 
  "BookCopy" instance.
  </code></pre>