snapshot.val() returning null, while there is data - node.js

Question

I am trying to retrieve information from Firebase Realtime Database, inside Dialogflow's inline editor using Google Assistant, However for some reason I'm getting back null, Google Assistant answers person1's Alex is null
Is my reference not targeting correctly? I'm using dialogflow and realtime database for the first time.
'use strict';
const functions = require('firebase-functions');
const {WebhookClient} = require('dialogflow-fulfillment');
const {Card, Suggestion} = require('dialogflow-fulfillment');
var admin = require('firebase-admin');
admin.initializeApp({
credential: admin.credential.cert({
projectId: ' ',
clientEmail: ' ',
privateKey: ' '
}),
databaseURL: 'https://*****.firebaseio.com'
});
process.env.DEBUG = 'dialogflow:debug';
// enables lib debugging statements
exports.dialogflowFirebaseFulfillment = functions.https.onRequest((request,response)=>{
const agent = new WebhookClient({
request,
response
});
console.log('Dialogflow Request headers: ' + JSON.stringify(request.headers));
console.log('Dialogflow Request body: ' + JSON.stringify(request.body));
function welcome(agent) {
agent.add(`Welcome to my agent!`);
}
function fallback(agent) {
agent.add(`I didn't understand`);
agent.add(`I'm sorry, can you try again?`);
}
function personFacts(agent) {
const personId = agent.parameters["personId"];
const personMeasurement = agent.parameters["personMeasurement"];
var db = admin.database();
var ref = db.ref(`person/${personId}/${personMeasurement}`);
return ref.once("value").then(snapshot=>{
var result = snapshot.val();
agent.add(`${personId}'s ${personMeasurement} is ${result}`);
}).catch(err=>{
agent.add('uh oh, something went wrong.');
console.error(err);
});
}
let intentMap = new Map();
intentMap.set('Default Welcome Intent', welcome);
intentMap.set('Default Fallback Intent', fallback);
intentMap.set('person', personFacts);
agent.handleRequest(intentMap);
});
Here is Realtime Database:
As suggested i changed numbers 0, 1, 2 into person1, person2, person3
for the reference to realtime database need little help :
function personFacts(agent) {
const personId = agent.parameters["personId"];
const personMeasurement = agent.parameters["personMeasurement"];
const pperson = person[personId];
const result = pperson[personMeasurement];
var db = admin.database();
var ref = db.ref(`person/${personId}/${personMeasurement}`);
return ref.once("value")
.then( snapshot => {
var result = snapshot.val();
agent.add(`${personId}'s ${personMeasurement} is ${result}`);
})
.catch( err => {
agent.add('uh oh, something went wrong.');
console.error( err );
});
}
let intentMap = new Map();
intentMap.set('Default Welcome Intent', welcome);
intentMap.set('Default Fallback Intent', fallback);
intentMap.set('person', personFacts);
agent.handleRequest(intentMap);
});

Answer 1

It sounds like you're asking for information by asking for "person 1", but there is no key in the database with the value "person1". There is a key "1" under the "person" hierarchy, and perhaps this is what you want.
You have a few options, depending what you're actually trying to do.
You can either change your keys to reflect what you're asking for. So instead of using "0" or "1" or "2" for your keys, you can just use "person1", or "person2", or "person3". You don't need to use numbers in the Firebase database. You can use however you want to reference the data.
Another alternative is to keep the keys in the database as you have, and when the person says "person1", to somehow map that to the correct key that is in the database (ie - "0"). You can write code to do this - in this case, you want a substring of the personId parameter. So perhaps something like
let personKey = personId.substring(6);
and then use personKey in your reference path
var ref = db.ref( `person/${personKey}/${personMeasurement}` );
However, these are just examples - how you do it depends on how you want to structure and access your data.
The important part is to understand how the Firebase database lets you access the data. Data is stored in a hierarchy, and we can think of each node in that hierarchy having a path to it. In your example, you have one node at the top named "person". Under that node, are several nodes that are just numbers - a node named "0" is one example. Under the "0" node, you have several nodes, including one named "Alex".
You can reference this specific "Alex" node by specifying the full reference path to it. We separate the name of each node with a "/". So the full reference path to this particular "Alex" would be person/0/Alex. To get the value at this node, we can build a ref object and then use once("value") to get the value just once (as opposed to listening to it for changes).
Since the "0" and "Alex" portions of this are stored in variables, we need to build a string that contains these values. One simple way to do this is to use a template literal or "backtick string" in JavaScript. In this type of string, everything inside a ${} is evaluated. So ${personKey} means to insert into the string the value of personKey.
So the line
var ref = db.ref( `person/${personKey}/${personMeasurement}` );
means "create a reference to a node the database, starting at the 'person' node, then finding the node under this that has the value in personKey, then find the node under that with the value in personMeasurement".
You can, of course, replace personKey and personMeasurement with whatever variables contain the values you'd be looking for at that point in the node hierarchy. You can build this string in other ways and build the reference using other tools. The important point is to understand that the reference is to a point in the database and that you need to build this reference before you can fetch the reference from this point.