Difference between event child_added of Realtime Database Firebase vs Firebase Cloud function

Question

I having a case where I need to receive notification whenever Realtime Database Firebase have new data. When investigate, I found out there are 2 way to do this in client side (mobile app using React Native):

• Using Realtime Database child_added event
• Using Cloud Functions event onWrite()

Can someone please tell me what is the difference between 2 way and pros and cons of each way?. The document is not helpful for me about this.

Note:

• Backend Server written in Java framework Spring boot response function push new data to Realtime Database Firebase.
• Client side need to receive notification when new data added to Realtime Database Firebase (currently only mobile app written in React Native but I also need to do it for web in the future)

Answer 1

Paraphrasing Frank Van Puffelen's comment as an answer:

Firestore and Realtime databases are two completely separate databases. Though firestore and Realtime database both are part of Firebase. If you want to trigger a cloud function from Real Time database, please follow this documentation. If you want to trigger cloud function from Firestore, please check this documentation.