firebase functions + realtime database - database structure and code

Question

I'm on a simple application: It's my first try with firebase functions + realtime database.

The functions are going to be called by an external client application (e.g.: android).

if it was not javascript + nosqldb I would not have a problem, but here I am stuck, because I'm not sure for the best db structure and about transaction-like operations.

I. stored data:

• user profile (id, fullname, email, phone, photo)
• tickets amount per user
• history for tickets buyings
• history for tickets usings

II. actions:

• user buy some tickets - should add tickets to the user's amount AND add a record to buyings history

• user use some tickets - should remove tickets from the user's amount AND add a record to usings history

So my base problem is this ANDs - if it was a SQL db i would use a transaction but here I'm not sure what is db structure and js code in order to achieve same result.

EDITED: ======== index.js =======

exports.addTickets = functions.https.onCall((data, context) => {
 // data comes from client app
 const buyingRecord = data;
 console.log(‘buyingRecord: ‘ + JSON.stringify(buyingRecord));

return tickets.updateTicketsAmmount(buyingRecord)
 .then((result)=>{
 tickets.addTicketsBuyingRecord(buyingRecord);
 result.userid = buyingRecord.userid;
 result.ticketsCount = buyingRecord.ticketsCount;
 return result;
 });
});

====== tickets.js =======

exports.updateTicketsAmmount = function(buyingRecord) {
 var userRef = db.ref(‘users/’ + buyingRecord.userid);
 var amountRef = db.ref(‘users/’ + buyingRecord.userid + ‘/ticketsAmount’);
 return amountRef.transaction((current)=>{
 return (current || 0) + buyingRecord.ticketsCount;
 })
 .then(()=>{
 console.log(“amount updated for userid [“ + buyingRecord.userid + “]”);
 return userRef.once(‘value’);
 })
 .then((snapshot)=>{
 var data = snapshot.val();
 console.log(“data for userid [“ + snapshot.key + “]:” + JSON.stringify(data));
 return data;
 });
}

exports.addTicketsBuyingRecord = function(buyingRecord) {
 var historyRef = db.ref(‘ticketsBuyingHistory’);
 var newRecordRef = historyRef.push();
 return newRecordRef.set(buyingRecord)
 .then(()=>{
 console.log(‘history record added.’); 
 return newRecordRef.once(‘value’);
 })
 .then((snapshot)=>{
 var data = snapshot.val();
 console.log(‘data:’ + JSON.stringify(data));
 return data;
 });
}

Answer 1

You would have to use the callback, the request on Android to add or read data have an onSuccess or OnFailure CallBack, i used this to trigger my new request.

You can check this on the doc here :)

Also if instead of using RealTime Database you use Firestore you can use the FireStore Transactions here is the info.