def add(self, product_id, unit_cost, quantity=1, **extra_data_dict):
"""
Returns True if the addition of the product of the given product_id and unit_cost with given quantity
is succesful else False.
Can also add extra details in the form of dictionary.
"""
product_dict = self.__product_dict(
unit_cost, quantity, extra_data_dict)
self.redis_connection.hset(
self.user_redis_key, product_id, Serializer.dumps(product_dict))
self.user_cart_exists = self.cart_exists(self.user_id)
self.set_ttl()
