How do I perform a dynamic Django queryset update?

I have the following model:

class Book(models.Model):
    title = models.CharField(max_length=100)
    quantity = models.IntegerField()
    in_stock = models.BooleanField()

I have a form which allows me to update the quantity and stock of multiple selected books:

Quantity:
In Stock:

List of Books:
1. Eat Pray and Love
2. Twilight

In my views, I can update a querylist of Books like the following:

quantity = form.cleaned_data['quantity']
in_stock = form.cleaned_data['in_stock']

if quantity:
    selected_books.update(quantity=quantity)

if in_开发者_Python百科stock:
    selected_books.update(in_stock=in_stock)

I am basically doing a batch update only if the field has been entered. The above requires 2 separate sql update statements. Is there a way to call use a single sql statement regardless of the number of entered fields?

---

Build a dict, then do it at once with kwarg expansion.

d = {}

if quantity:
  d['quantity'] = quantity

 ...

selected_books.update(**d)