Adding aggregation function to repo

Author: samtstern

firestore/solution-aggregation/functions/index.js

@@ -0,0 +1,34 @@
+const functions = require('firebase-functions');
+const admin = require('firebase-admin');
+
+const db = admin.firestore();
+
+// [START aggregate_function]
+exports.aggregateRatings = functions.firestore
+    .document('restaurants/{restId}/ratings/{ratingId}')
+    .onWrite((change, context) => {
+      // Get value of the newly added rating
+      var ratingVal = change.after.data().rating;
+
+      // Get a reference to the restaurant
+      var restRef = db.collection('restaurants').document(context.params.restId);
+
+      // Update aggregations in a transaction
+      return db.runTransaction(transaction => {
+        return transaction.get(restRef).then(restDoc => {
+          // Compute new number of ratings
+          var newNumRatings = restDoc.data('numRatings') + 1;
+
+          // Compute new average rating
+          var oldRatingTotal = restDoc.data('avgRating') * restDoc.data('numRatings');
+          var newAvgRating = (oldRatingTotal + ratingVal) / newNumRatings;
+
+          // Update restaurant info
+          return transaction.update(restRef, {
+            avgRating: newAvgRating,
+            numRatings: newNumRatings
+          });
+        });
+      });
+    });
+// [END aggregate_function]

firestore/solution-aggregation/functions/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "solution-aggregation",
+  "description": "Cloud Functions for Firebase",
+  "scripts": {
+    "serve": "firebase serve --only functions",
+    "shell": "firebase experimental:functions:shell",
+    "start": "npm run shell",
+    "deploy": "firebase deploy --only functions",
+    "logs": "firebase functions:log"
+  },
+  "dependencies": {
+    "firebase-admin": "~5.8.1",
+    "firebase-functions": "^1.0.1"
+  },
+  "private": true
+}