Maximum number of roundtrips for pushing to a list of data in Firebase Real Time Database?

Question

In my angular 4 application I use the push() method to append data to a list of data in Firebase Realtime Database. See Firebase documentation: https://firebase.google.com/docs/database/web/lists-of-data

The push() method generates a unique key every time a new child is added to the specified Firebase reference. This is an Array 'market' that consists of 250 objects with the keys symbol, price, balance:

market = [
  { symbol: '1ST', price_usd: 1, balance: 100},
  { symbol: '2ND', price_usd: 2, balance: 300},
  { symbol: '3RD', price_usd: 3, balance: 400}
  // etc etc for a total of 250 objects
];

I have written the following code in my Angular 4 component:

import {AngularFireDatabase} from 'angularfire2/database';
import * as firebase from 'firebase';

constructor(private db: AngularFireDatabase) {}

storeTicker() {
  const timestamp = firebase.database.ServerValue.TIMESTAMP;
  for (let object of market) {
    const path = object['symbol'];
    const itemsRef = this.db.list('Tickers/' + path);
    itemsRef.push({ symbol: path, price_usd: object['price_usd'], balance: object['balance'], time: timestamp});
  }
}

The code is executed when a button is clicked, this will result in a time-series for each reference.

My Firebase Realtime Database looks like this:

{ "Tickers" : {
    "1ST" : {
      "-Kx8gN5uZALd5BP2GCH6" : {
        "balance" : 0,
        "price_usd" : 0.25583,
        "symbol" : "1ST",
        "time" : 1508769890908
       }},
    "2ND" : {
      "-Kx8Z0xCl7ONZERk1ICo" : {
        "balance" : 0,
        "price_usd" : 0.0253829,
        "symbol" : "2ND",
        "time" : 1508769890908
      }},
    "3RD" : {
      "-Kx8gN5FEZEPsOe8S-Tw" : {
        "balance" : 0,
        "price_usd" : 0.767354,
        "symbol" : "3RD",
        "time" : 1508769890908
    }},
  // for a  total of 250 paths
}}

Each call to push() in this way will result in a roundtrip to Firebase. The problem is that Firebase only does push() for the first 100 references.

I can't find a limit on the number of roundtrips in the Firebase documentation: https://firebase.google.com/docs/database/usage/limits

I found one question on Stackoverflow Adding list of data in Firebase with a similar problem but I don't understand the update part.

My 2 questions are:

1. Is there a maximum number of roundtrips in Firebase or is there some other error?

2. How can I make my code work, by combining it into a multi-location update?

Answer 1

Using the push() method with no arguments will generate a unique ID locally and not result in a network operation to the database:

If you provide a value to push(), the value will be written to the generated location. If you don't pass a value, nothing will be written to the Database and the child will remain empty (but you can use the Reference elsewhere).

So, you could use this to obtain a unique ID for each item you need to push to the database, store this in an array and then use update() to send all items to the database simultaneously in a multi-location update, something like:

storeTicker() {
  const timestamp = firebase.database.ServerValue.TIMESTAMP;
  var updates = {};
  for (let object of market) {
    const key = this.db.list('/Tickers').push().key; // Get a new unique key (locally, no network activity)
    const path = object['symbol'] + '/' + key;
    updates[path] = {symbol: object['symbol'], price_usd: object['price_usd'], balance: object['balance'], time: timestamp};
  }
  this.db.object('/Tickers').update(updates);
}

The update() method (similar to the official Firebase JavaScript SDK update() method) works by sending the entire array to the specified location:

The values argument contains multiple property-value pairs that will be written to the Database together. Each child property can either be a simple property (for example, "name") or a relative path (for example, "name/first") from the current location to the data to update.

For a documentation example of this, see updating data using AngularFire or update specific fields using the JavaScript SDK.