Merge pull request #54 from fraktalio/feature/view_merge

Added new `merge`/`combine` function for the View

src/view.rs

@@ -127,6 +127,7 @@ impl<'a, S, E> View<'a, S, E> {
 
     /// Combines two views into one.
     /// Creates a new instance of a View by combining two views of type `S`, `E` and `S2`, `E2` into a new view of type `(S, S2)`, `Sum<E, E2>`
+    /// Combines two views that operate on different event types (`E`` and `E2``) into a new view operating on `Sum<E, E2>`
     pub fn combine<S2, E2>(self, view2: View<'a, S2, E2>) -> View<'a, (S, S2), Sum<E, E2>>
     where
         S: Clone,
@@ -156,6 +157,36 @@ impl<'a, S, E> View<'a, S, E> {
             initial_state: new_initial_state,
         }
     }
+
+    /// Merges two views into one.
+    /// Creates a new instance of a View by merging two views of type `S`, `E` and `S2`, `E` into a new view of type `(S, S2)`, `E`
+    /// Similar to `combine`, but the event type is the same for both views.
+    /// Composes two views that operate on the same/shared event type (`E`) into a new view operating on `E`
+    pub fn merge<S2>(self, view2: View<'a, S2, E>) -> View<'a, (S, S2), E>
+    where
+        S: Clone,
+        S2: Clone,
+    {
+        let new_evolve = Box::new(move |s: &(S, S2), e: &E| {
+            let s1 = &s.0;
+            let s2 = &s.1;
+
+            let new_state = (self.evolve)(s1, e);
+            let new_state2 = (view2.evolve)(s2, e);
+            (new_state, new_state2)
+        });
+
+        let new_initial_state = Box::new(move || {
+            let s1 = (self.initial_state)();
+            let s2 = (view2.initial_state)();
+            (s1, s2)
+        });
+
+        View {
+            evolve: new_evolve,
+            initial_state: new_initial_state,
+        }
+    }
 }
 
 /// Formalizes the `State Computation` algorithm for the `view` to handle events based on the current state, and produce new state.

tests/api/mod.rs

@@ -22,6 +22,15 @@ pub struct OrderViewState {
     pub is_cancelled: bool,
 }
 
+/// A second version of the ViewOrder entity / It represents the Query Model
+#[derive(Debug, Clone, PartialEq)]
+pub struct OrderView2State {
+    pub order_id: u32,
+    pub customer_name: String,
+    pub items: Vec<String>,
+    pub is_cancelled: bool,
+}
+
 /// All variants of Order commands
 #[derive(Debug, Clone, PartialEq)]
 #[allow(dead_code)]

tests/view_test.rs

@@ -1,3 +1,4 @@
+use api::OrderView2State;
 use fmodel_rust::view::{View, ViewStateComputation};
 
 use crate::api::{
@@ -61,14 +62,45 @@ fn shipment_view<'a>() -> View<'a, ShipmentViewState, ShipmentEvent> {
     }
 }
 
+fn order_view_second<'a>() -> View<'a, OrderView2State, OrderEvent> {
+    View {
+        evolve: Box::new(|state, event| {
+            let mut new_state = state.clone();
+            match event {
+                OrderEvent::Created(evt) => {
+                    new_state.order_id = evt.order_id;
+                    new_state.customer_name = evt.customer_name.to_owned();
+                    new_state.items = evt.items.to_owned();
+                }
+                OrderEvent::Updated(evt) => {
+                    new_state.items = evt.updated_items.to_owned();
+                }
+                OrderEvent::Cancelled(_) => {
+                    new_state.is_cancelled = true;
+                }
+            }
+            new_state
+        }),
+        initial_state: Box::new(|| OrderView2State {
+            order_id: 0,
+            customer_name: "".to_string(),
+            items: Vec::new(),
+            is_cancelled: false,
+        }),
+    }
+}
+
 #[test]
 fn test() {
     let order_view: View<OrderViewState, OrderEvent> = order_view();
     let order_view2: View<OrderViewState, OrderEvent> = crate::order_view();
+    let order_view3: View<OrderViewState, OrderEvent> = crate::order_view();
+    let order_view_second: View<OrderView2State, OrderEvent> = order_view_second();
     let shipment_view: View<ShipmentViewState, ShipmentEvent> = shipment_view();
     let combined_view = order_view2
         .combine(shipment_view)
         .map_event(&event_from_sum);
+    let merged_view = order_view3.merge(order_view_second);
 
     let order_created_event = OrderEvent::Created(OrderCreatedEvent {
         order_id: 1,
@@ -91,6 +123,7 @@ fn test() {
         customer_name: "John Doe".to_string(),
         items: vec!["Item 1".to_string(), "Item 2".to_string()],
     });
+
     let new_combined_state2 = combined_view.compute_new_state(None, &[&order_created_event2]);
     assert_eq!(
         new_combined_state2,
@@ -110,6 +143,25 @@ fn test() {
         )
     );
 
+    let new_combined_state_2 = merged_view.compute_new_state(None, &[&order_created_event]);
+    assert_eq!(
+        new_combined_state_2,
+        (
+            OrderViewState {
+                order_id: 1,
+                customer_name: "John Doe".to_string(),
+                items: vec!["Item 1".to_string(), "Item 2".to_string()],
+                is_cancelled: false,
+            },
+            OrderView2State {
+                order_id: 1,
+                customer_name: "John Doe".to_string(),
+                items: vec!["Item 1".to_string(), "Item 2".to_string()],
+                is_cancelled: false,
+            }
+        )
+    );
+
     let shipment_created_event2 = Event::ShipmentCreated(ShipmentCreatedEvent {
         shipment_id: 1,
         order_id: 1,