feat: SAGA

package.json

@@ -6,11 +6,15 @@
     "start": "cds-serve"
   },
   "dependencies": {
-    "@cap-js/hana": ">=2.1.2",
     "@sap/cds": ">=9"
   },
   "devDependencies": {
     "@cap-js/sqlite": ">=2"
   },
+  "cds": {
+    "requires": {
+      "messaging": true
+    }
+  },
   "license": "Apache-2.0"
 }

srv/data-service.cds

@@ -30,7 +30,8 @@ service FlightsService {
   // Custom actions and events to sync with consumers about flight seat availability
   action BookingCreated ( flight: Flights:ID, date: Flights:date, seats: array of Integer);
   action BookingDeleted ( flight: Flights:ID, date: Flights:date, seats: array of Integer);
-  event FlightsUpdated  { flight: Flights:ID; date: Flights:date; free_seats: Integer; }
+  // Restrict payload to identity as messages can overtake each other in the ether
+  event FlightsUpdated  { flight: Flights:ID; date: Flights:date; };
 }
 
 

srv/data-service.js

@@ -5,14 +5,18 @@ class DataService extends cds.ApplicationService { init() {
 
   this.on ('BookingCreated', async req => {
     const { flight, date, seats = [null] } = req.data
-    await UPDATE (Flights, { flight_ID:flight, date }) 
-    .set `occupied_seats = occupied_seats + ${seats.length}`
+    const confirmed = await UPDATE (Flights, { flight_ID:flight, date })
+      .set `occupied_seats = occupied_seats + ${seats.length}`
+      .where `free_seats >= ${seats.length}`
+    if (!confirmed) req.reject('Flight is fully booked')
+    this.emit('FlightsUpdated', { flight, date })
   })
 
   this.on ('BookingDeleted', async (req) => {
     const { flight, date, seats = [null] } = req.data
-    await UPDATE (Flights, { flight_ID:flight, date }) 
-    .set `occupied_seats = occupied_seats - ${seats.length}`
+    await UPDATE (Flights, { flight_ID:flight, date })
+      .set `occupied_seats = occupied_seats - ${seats.length}`
+    this.emit('FlightsUpdated', { flight, date })
   })
 
   return super.init()