In Cloud function how can i join from another collection to get data?

Question

I am using Cloud Function to send a notification to mobile device. I have two collection in Firestore clientDetail and clientPersonalDetail. I have

Answer 1

But I need ClientID not name to show in notification so I'll have to join to clientPersonal collection in order to get name using clientID. What should do ?

Unfortunately, there is no JOIN clause in Firestore. Queries in Firestore are shallow. This means that they only get items from the collection that the query is run against. There is no way to get documents from two top-level collection in a single query. Firestore doesn't support queries across different collections in one go. A single query may only use properties of documents in a single collection.

How can I create another function which solely return name by passing clientID as argument, and waits until it returns the name.

So the most simple solution I can think of is to first query the database to get the clientID. Once you have this id, make another database call (inside the callback), so you can get the corresponding name.

Another solution would be to add the name of the user as a new property under ClientDetail so you can query the database only once. This practice is called denormalization and is a common practice when it comes to Firebase. If you are new to NoQSL databases, I recommend you see this video, Denormalization is normal with the Firebase Database for a better understanding. It is for Firebase realtime database but same rules apply to Cloud Firestore.

Also, when you are duplicating data, there is one thing that need to keep in mind. In the same way you are adding data, you need to maintain it. With other words, if you want to update/detele an item, you need to do it in every place that it exists.