in app/helpers/carts/helpers.py [0:0]
def add_to_cart(uid, item_id):
"""
Helper function for adding an item to a cart.
Parameters:
uid (str): The unique ID of an user.
item_id (str): The ID of an item.
Output:
None.
"""
item = CartItem(
uid=uid,
item_id=item_id,
modify_time=int(time.time()))
firestore_client.collection('carts').document().set(asdict(item))