How I can copy One Firebase Collection to Another Firebase Collection in Android

Question

As you can there are 3 collections in my Firestore database:

1. Plans
2. UPIs
3. Users

Upon Successful Signup of a user, I want to copy all the values present in Plans Collection to Users Collection under their mobile number as a document.

Answer 1

There is currently no straightforward solution for that. The single option that you have, is to move each and every document that exists in the "Plans" collection, to any other collection of your choice.

If you want the "Plans" to be a subcollection under the user's mobile number document in the "Users" collection, then you need to have a schema similar to this:

Firestore-root
  |
  --- Users (collection)
       |
       --- $phoneNumber (document) //
            |
            --- Plans (Sub-collection)
                 |
                 --- $planId
                       |
                       --- //fields

This operation can be done on the client, or using a trusted environment you control. The latter is obviously more recommended. So you might consider using Cloud Functions for Firebase, to trigger a function on user creation that does exactly that.