Using onWrite Trigger for Realtime database in Firebase function

Question

I designed a flutter application using dart and firebase backend. I want to get triggered when a user creates, delete, or updates anything in the database. I understood onCreate,onRemoved, and onUpdate methods. I wrote a javascript code in the firebase cloud function. I need to send a notification when a trigger happens. I don't want to use 3 different triggers. I want to use onWrite trigger only.

This is my database.

There are four departments called comp, civil, elect, and mech. I want to get triggered when database changes happen in a single onWrite trigger!

My First question is, I want to differentiate whether it is created or delete or update from onWrite trigger. I know it will trigger for all 3 events. But how can I differentiate it?

This is my code for onCreate...

exports.noticeAddedComp = functions.database.ref('main/notices/comp/{id}').onCreate( async evt =>  {

var token = ['dxnfr3dq6_Y:APA91bHavtoP62l296qzVoBhzQJbMFA']
const payload = {
    notification:{
        title : 'Message from Cloud',
        body : 'This is your body',
        sound : 'default'
    },
    data:{
    message : 'Thi is new Push',
    click_action : 'FLUTTER_NOTIFICATION_CLICK',
    }
};
        await admin.messaging().sendToDevice(token,payload);

});

Above code is working. But it is for onCreate.

My second question is, Do I need to write four onWrite trigger codes for four departments?

Frank van Puffelen Frank van Puffelen · Accepted Answer · 2020-05-09T14:29:40

You can use the change.before and change.after properties to determine whether the node was created, deleted, or updated in a onWrite handler:

exports.noticeAddedComp = functions.database.ref('main/notices/comp/{id}')
.onWrite( async (change, context) =>  {
  if (!change.before.exists()) console.log("New node: "+change.after.key);
  if (!change.after.exists()) console.log("Deleted node: "+change.before.key);
  if (change.before.exists() && change.after.exists()) console.log("Updated node: "+change.after.key)
  ...
});

You can attach a Cloud Function to all departments at once, by including another parameter into its path:

exports.noticeAddedComp = functions.database.ref('main/notices/{dept}/{id}')
.onWrite( async (change, context) =>  {
  console.log("Triggered for department: "+context.params.dept);
  ...
})

Using onWrite Trigger for Realtime database in Firebase function

2 Answers