Update README.md

README.md

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-# Final state of exercise 1 for CAA265 - Rapid Service Development with SAP Cloud Application Programming Model
+# Final state after exercise 2 for CAA265 - Rapid Service Development with SAP Cloud Application Programming Model
 
 **DO NOT MERGE IN MASTER**

packages/.cdsrc.json

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-{
-  "cds_version": "^3.17.4"
-}

packages/reviews-service/.cdsrc.json

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+{
+    "build": {
+        "target": ".",
+        "tasks": []
+    }
+}

packages/reviews-service/.gitignore

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+.che/
+.gen/
+gen/
+mta_archives/
+node_modules/
+target/
+
+.cds_gen.log
+connection.properties
+*.db
+.DS_Store
+*.orig
+_out
+default-*.json
+package-lock.json

packages/reviews-service/.vscode/launch.json

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+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "cds run",
+            "request": "launch",
+            "type": "node", "runtimeExecutable": "npx","runtimeArgs": [ "-n" ],
+            "args": [ "--","cds","run","--in-memory?" ], // the leading "--" arg ensures it works with as well as without debugging
+            "console": "integratedTerminal",
+            "skipFiles": [ "<node_internals>/**" ]
+        }
+    ]
+}

packages/reviews-service/db/schema.cds

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+namespace sap.capire.reviews;
+using { User } from '@sap/cds/common';
+
+// Reviewed subjects can be any entity that is uniquely identified
+type ReviewedSubject : String(111);
+
+entity Reviews {
+  key ID   : String(36);
+  subject  : ReviewedSubject;
+  reviewer : User;
+  rating   : Rating;
+  title    : String(111);
+  text     : String(1111);
+  date     : DateTime;
+  likes    : Composition of many Likes on likes.review = $self;
+  liked    : Integer default 0; // counter for likes as helpful review (count of all _likes belonging to this review)
+}
+
+type Rating : Integer enum {
+  Best  = 5;
+  Good  = 4;
+  Avg   = 3;
+  Poor  = 2;
+  Worst = 1;
+}
+
+entity Likes {
+  key review : Association to Reviews;
+  key user   : User;
+}

packages/reviews-service/index.cds

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+using from './srv/reviews-service';

packages/reviews-service/package.json

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+{
+    "name": "reviews-service",
+    "version": "1.0.0",
+    "description": "Generated by cds init",
+    "repository": "<Add your repository here>",
+    "license": "ISC",
+    "dependencies": {
+        "@sap/cds": "^3.17.4",
+        "express": "^4.17.1"
+    },
+    "engines": {
+        "node": "^8.9"
+    },
+    "scripts": {
+        "build": "cds build/all --clean",
+        "deploy": "cds deploy",
+        "start": "cds run"
+    }
+}

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

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+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

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+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}.`)
+    })
+  })
+})