How to compose functions that return Option[List] in Scala?

Question

Suppose I have two functions to get orders and order items:

def getOrders(): Option[List[Int]] = ...
def getOrderItems(orderId: Int): Option[List[Int]] = ...
         


        

Answer 1

The simplest modification I could think of is as below:

for{
    orderId <- getOrders.getOrElse(Nil)
    items <- getOrderItems(orderId)
} yield items

The for comprehension uses the first statement to determins the rest the types. For instance in the above the type List[Int] would be infered and this is different from Option[List[Int]].