Cloud Functions for Firebase write operation inside a DB event function

Question

I'm currently trying to learn Firebase functions. This new feature seems to be pretty powerful and useful.

I'd like to use a function the catch a DB writing event, make a comparison with a specific location in DB and then write some data (depending on the comparison result) in another location in DB.

Here's my current Node.js code:

exports.verificaFineLavoro = functions.database.ref('/Aziende/{nomeazienda}/LogAsegno/{pushidbracciante}/{pushidlog}/Asegno')
.onWrite(event => {
  const original = event.data.val();
  console.log('VerificaFineLavoro', event.params.pushId, original);
  const aSegno = original;
  console.log('aSegno', aSegno +"");
  const FineLavoro = ref.parent.parent.parent.parent.child("Asegno/"+aSegno+"/FineLavoro");
  return event.data.ref.child('FL').set(FineLavoro);
});

Currently the function gets triggered but it stops working because of the references which are probably wrong.

If you already know that your references are wrong, what keeps you from fixing them? — Frank van Puffelen
– Frank van Puffelen, Commented Apr 4, 2017 at 13:18
I don't know how to make a reference inside a function and how to retrive data from it. The code i posted was an attemp. — L. Gangemi
– L. Gangemi, Commented Apr 4, 2017 at 13:29

Frank van Puffelen · Accepted Answer · 2017-04-04 16:07:16Z

4

The Cloud Functions for Firebase documentation on triggering from the database contains code snippets that show how to access other nodes in the database.

For example, this snippet sets a value as a sibling to the node that triggered the function:

return event.data.ref.parent.child('uppercase').set(uppercase);

Here's another snippet from the sample on counting child nodes:

exports.countlikechange = 
functions.database.ref('/posts/{postid}/likes/{likeid}').onWrite(event => {
  const collectionRef = event.data.ref.parent;
  const countRef = collectionRef.parent.child('likes_count');
  ...

To access the root of the database use event.data.ref.root (to access the root node with the permissions of the user that triggered the function) or event.data.adminRef.root (to access the root with full administrative permission).

edited Apr 4, 2017 at 16:07

answered Apr 4, 2017 at 13:39

Frank van Puffelen

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6 Comments

L. Gangemi Over a year ago

Thank you, I'm going to try it now ;)

L. Gangemi Over a year ago

How can i build a reference from the root of my db?

Doug Stevenson Over a year ago

event.data.ref.root or event.data.adminRef.root

Rahul Sainani Over a year ago

@L.Gangemi You can also do admin.database().ref('path/to/ref') to reference some other path.

L. Gangemi Over a year ago

Can i use more .parent in sequence? I'd like to get the event reference and go back to a node at the start

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