Added merge function for the Saga, next to the combine

src/saga.rs

@@ -131,6 +131,25 @@ impl<'a, AR, A> Saga<'a, AR, A> {
 
         Saga { react: new_react }
     }
+
+    /// Merges two sagas into one.
+    /// Creates a new instance of a Saga by merging two sagas of type `AR`, `A` and `AR`, `A2` into a new saga of type `AR`, `Sum<A, A2>`
+    pub fn merge<A2>(self, saga2: Saga<'a, AR, A2>) -> Saga<'a, AR, Sum<A2, A>> {
+        let new_react = Box::new(move |ar: &AR| {
+            let a: Vec<Sum<A2, A>> = (self.react)(ar)
+                .into_iter()
+                .map(|a: A| Sum::Second(a))
+                .collect();
+            let a2: Vec<Sum<A2, A>> = (saga2.react)(ar)
+                .into_iter()
+                .map(|a2: A2| Sum::First(a2))
+                .collect();
+
+            a.into_iter().chain(a2).collect()
+        });
+
+        Saga { react: new_react }
+    }
 }
 
 /// Formalizes the `Action Computation` algorithm for the `saga` to handle events/action_results, and produce new commands/actions.

tests/saga_test.rs

@@ -30,6 +30,30 @@ fn order_saga<'a>() -> Saga<'a, OrderEvent, ShipmentCommand> {
     }
 }
 
+fn order_saga_2<'a>() -> Saga<'a, Event, ShipmentCommand> {
+    Saga {
+        react: Box::new(|event| match event {
+            Event::OrderCreated(evt) => {
+                vec![ShipmentCommand::Create(CreateShipmentCommand {
+                    shipment_id: evt.order_id,
+                    order_id: evt.order_id,
+                    customer_name: evt.customer_name.to_owned(),
+                    items: evt.items.to_owned(),
+                })]
+            }
+            Event::OrderUpdated(_) => {
+                vec![]
+            }
+            Event::OrderCancelled(_) => {
+                vec![]
+            }
+            Event::ShipmentCreated(_) => {
+                vec![]
+            }
+        }),
+    }
+}
+
 fn shipment_saga<'a>() -> Saga<'a, ShipmentEvent, OrderCommand> {
     Saga {
         react: Box::new(|event| match event {
@@ -43,15 +67,44 @@ fn shipment_saga<'a>() -> Saga<'a, ShipmentEvent, OrderCommand> {
     }
 }
 
+fn shipment_saga_2<'a>() -> Saga<'a, Event, OrderCommand> {
+    Saga {
+        react: Box::new(|event| match event {
+            Event::ShipmentCreated(evt) => {
+                vec![OrderCommand::Update(UpdateOrderCommand {
+                    order_id: evt.order_id,
+                    new_items: evt.items.to_owned(),
+                })]
+            }
+
+            Event::OrderCreated(_) => {
+                vec![]
+            }
+            Event::OrderUpdated(_) => {
+                vec![]
+            }
+            Event::OrderCancelled(_) => {
+                vec![]
+            }
+        }),
+    }
+}
+
 #[test]
 fn test() {
     let order_saga: Saga<OrderEvent, ShipmentCommand> = order_saga();
     let order_saga2: Saga<OrderEvent, ShipmentCommand> = crate::order_saga();
+    let order_saga_2: Saga<Event, ShipmentCommand> = crate::order_saga_2();
     let shipment_saga: Saga<ShipmentEvent, OrderCommand> = shipment_saga();
+    let shipment_saga_2: Saga<Event, OrderCommand> = crate::shipment_saga_2();
     let combined_saga = order_saga2
         .combine(shipment_saga)
         .map_action(&sum_to_command)
         .map_action_result(&event_from_sum);
+    let merged_saga = order_saga_2
+        .merge(shipment_saga_2)
+        .map_action(&sum_to_command);
+
     let order_created_event = OrderEvent::Created(OrderCreatedEvent {
         order_id: 1,
         customer_name: "John Doe".to_string(),
@@ -72,6 +125,7 @@ fn test() {
         customer_name: "John Doe".to_string(),
         items: vec!["Item 1".to_string(), "Item 2".to_string()],
     });
+
     let combined_commands = combined_saga.compute_new_actions(&order_created_event2);
     assert_eq!(
         combined_commands,
@@ -82,4 +136,15 @@ fn test() {
             items: vec!["Item 1".to_string(), "Item 2".to_string()],
         })]
     );
+
+    let merged_commands = merged_saga.compute_new_actions(&order_created_event2);
+    assert_eq!(
+        merged_commands,
+        [Command::ShipmentCreate(CreateShipmentCommand {
+            shipment_id: 1,
+            order_id: 1,
+            customer_name: "John Doe".to_string(),
+            items: vec!["Item 1".to_string(), "Item 2".to_string()],
+        })]
+    );
 }