Django bulk price updates: update() with F() and bulk_update() from a CSV

# ======================================================================
# Q: Increase the price of all products in a category by 5%, and update 100,000
# products from a CSV.
#
# update() and bulk_update() do not call save() or signals, and do not update
# auto_now fields. You need to say this. For new rows: bulk_create(...,
# update_conflicts=True, unique_fields=['sku'], update_fields=['price']), which
# does an upsert.
# ======================================================================

# A single UPDATE in the database, without loading objects
Product.objects.filter(category=cat).update(price=F('price') * Decimal('1.05'))

# From CSV: bulk_update in batches
by_sku = {row['sku']: Decimal(row['price']) for row in csv.DictReader(f)}
products = list(Product.objects.filter(sku__in=by_sku).only('id', 'sku', 'price'))
for p in products:
    p.price = by_sku[p.sku]
Product.objects.bulk_update(products, ['price'], batch_size=1000)