Can't determine Firebase Database URL when trying to read Firebase Database from within Node.js Firebase function

Question

I am using Flutter to build an app that accesses the Firebase database. All good from the Flutter side....but I am new to Node.js and Cloud Functions. I am trying to create a Node.js function to react to a deletion event of a record on one Firebase Database node and then delete records from two other Firebase Database nodes and image files from Firestore.

I am reacting to the trigger event with a functions.database.onDelete call, no problem, but falling at the very next hurdle i.e.trying to read admin.database to get a snapshot.

I have created a dummy function that uses .onUpdate to pick up a trigger event (don't want to keep having to recreate my data as I would if I used .onDelete) and then tries to read my Firebase Database to access a different node. The trigger event is picked up fine but I don't seem to have a database reference Url to do the read...yet it is the same database. Output on the console log from a call to process.env.FIREBASE_CONFIG shows the Url is present.

The included function code also has commenting to show the various outputs I get on the console log.

I am going crazy over this.....PLEASE can anyone tell me where I am going wrong. Been searching Google, Stackoverflow, Firebase docs for the last two days :-(

const admin = require("firebase-admin"); // Import Admin SDK
const functions = require("firebase-functions"); // Import Cloud Functions

admin.initializeApp({
  credential: admin.credential.cert(
    require("./user-guy-firebase-adminsdk.json")
  )
});

exports.testDeleteFunction = functions.database
  .ref("/user-guys/{userGuyId}")
  // Using .onUpdate as I don't want to keep restoring my data if I use .onDelete
  .onUpdate((snapshot, context) => {

    const userData = snapshot.after.val();
    const userId = userData.userId;

    console.log('userId: ' + userId);         // Gives correct console log output: userId: wajzviEcUvPZEcMUbbkPzcw64MB2

    console.log(process.env.FIREBASE_CONFIG);
    // Gives correct console log output:
    // {"projectId":"user-guy","databaseURL":"https://user-guy.firebaseio.com","storageBucket":"user-guy.appspot.com","cloudResourceLocation":"us-central"}


    // I have tried each of the four following calls and received the console log message as indicated after each.
    // 
    // var root = admin.database.ref();       // Console Log Message: TypeError: admin.database.ref is not a function
    // var root = admin.database().ref();     // Console Log Message: Error: Can't determine Firebase Database URL.
    // var root = admin.database.ref;         // Fails at line 31 below with the message indicated.
    // var root = admin.database().ref;       // Console Log Message: Error: Can't determine Firebase Database URL.

    console.log(root.toString);               // Console Log Message: TypeError: Cannot read property 'toString' of undefined.

    // This is intended to read a chat thread for two users but processing never gets here.
    var database = root.child('chats').child('0cSLt3Sa0FS26QIvOLbin6MFsL43GUPYmmAg9UUlRLnW97jpMCAkEHE3');

    database
      .once("value")
      .then(snapshot => {
        console.log(snapshot.val());
      }, function (errorObject) {
        console.log("The read failed: " + errorObject.code);
      });
    return null; // Will do stuff here once working.
  });

Error messages shown in code comments.

Answer 1

If you want to use the configuration in FIREBASE_CONFIG, you should initialize the Admin SDK with no parameters:

admin.initializeApp();

This will use the default service account for your project, which should have full read and write access to the database.

Answer 2

You need to add your database url in admin.initializeApp

 admin.initializeApp({
 databaseURL:"your_database_url"
  });

Answer 3

select Realtime Database in firebase and copy your url add in settings in fire config or watch this video https://www.youtube.com/watch?v=oOm_9y3vb80

config example

const config = {
  apiKey: "",
  authDomain: "",
  projectId: "",
  databaseURL: "https://youUrl.firebaseio.com/",
  storageBucket: "",
  messagingSenderId: "",
  appId: "",
  measurementId: ""
};