final state of exercise 2

packages/reviews-service/srv/reviews-service.cds

@@ -0,0 +1,26 @@
+namespace sap.capire.reviews;
+using { sap.capire.reviews as my } from '../db/schema';
+
+service ReviewsService {
+
+  event reviewed : { subject:String; rating: Decimal(2,1) };
+
+  // API
+  entity Reviews as projection on my.Reviews excluding { likes }
+  action like (review:Reviews.ID);
+  action unlike (review:Reviews.ID);  
+
+  // Input validation
+  annotate Reviews with {
+    subject  @mandatory;
+    title    @mandatory;
+    rating   @mandatory @assert.enum;
+  }
+
+  // Auto-fill reviewers and review dates
+  annotate Reviews with {
+    reviewer @cds.on.insert:$user;
+    date     @cds.on.insert:$now;
+    date     @cds.on.update:$now;
+  }
+}

packages/reviews-service/srv/reviews-service.js

@@ -0,0 +1,40 @@
+const cds = require('@sap/cds')
+module.exports = cds.service.impl((srv) => {
+
+  // Get the CSN definition for Reviews from the db schema for sub-sequent queries
+  // ( Note: we explicitly specify the namespace to support embedded reuse )
+  const { Reviews, Likes } = cds.entities('sap.capire.reviews')
+
+  // Increment counter for reviews considered helpful
+  srv.on ('like', (req) => {
+     if (!req.user)  return req.reject(400, 'You must be identified to like a review')
+     const {review} = req.data, {user} = req
+     const tx = cds.transaction(req)
+     return tx.run ([
+       INSERT.into (Likes) .entries ({review_ID: review, user: user.id}),
+       UPDATE (Reviews) .set({liked: {'+=': 1}}) .where({ID:review})
+     ]).catch(() => req.reject(400, 'You already liked that review'))
+  })
+
+  // Delete a former like by the same user
+  srv.on('unlike', async (req) => {
+      if (!req.user) return req.reject(400, 'You must be identified to remove a former like of yours')
+      const { review } = req.data, { user } = req
+      const tx = cds.transaction(req)
+      const affectedRows = await tx.run(DELETE.from(Likes).where({ review_ID: review, user: user.id }))
+      if (affectedRows === 1) return tx.run(UPDATE(Reviews).set({ liked: { '-=': 1 } }).where({ ID: review }))
+   })
+
+  // Emit an event to inform subscribers about new avg ratings for reviewed subjects
+  // ( Note: req.on.succeeded ensures we only do that if there's no error )
+  srv.after(['CREATE', 'UPDATE', 'DELETE'], 'Reviews', async (_, req) => {
+    const { subject } = req.data
+    const { rating } = await cds.transaction(req).run(
+      SELECT.one(['avg(rating) as rating']).from(Reviews).where({ subject })
+    )
+    req.on('succeeded', () => {
+      srv.emit('reviewed', { subject, rating })
+      console.log(`Reviewed event was emitted for book "${subject}" with rating ${rating}.`)
+    })
+  })
+})