Adding a map to an array on Firestore Android

Question

I'm having a little trouble getting my data to save to a Firestore database. Each document in my "meetings" collection has a list of users (maps), but I cannot seem to add anything or create a new document. I read the documentation, and it said to use FieldValue.arrayUnion(), which I tried:

    private fun addUserToMeeting(user: User) {
        val meetingRef = database.collection("meetings").document(meetingID.toString())

        val userData = hashMapOf(
            "email" to user.email,
            "latitude" to user.latitude,
            "longitude" to user.longitude,
            "token" to user.token,
            "username" to user.username
        )

        meetingRef.update("users", FieldValue.arrayUnion(userData))
    }

This is called anytime an "add user to meeting" button is clicked.

Here's a picture of my schema:

Has anyone got some suggestions on what I might be doing wrong?

What isn't working about the code? It might be easiest to explain if you show a "before" and "after" screenshot of the document when you code has run. — Frank van Puffelen
– Frank van Puffelen, Commented Nov 13, 2021 at 23:23
@FrankvanPuffelen It's not doing anything at all. When I run it (by clicking), there's no meeting document or anything. It's as if no updates have happened whatsoever. The "meeting" under the "exampleUUIDForMeeting" was created just to see if I was connected, which is a little shrewd, but it worked in a pinch; it doesn't contain any valuable information. — cjames
– cjames, Commented Nov 13, 2021 at 23:30

Frank van Puffelen · Accepted Answer · 2021-11-13 23:39:02Z

4

If the document doesn't exist yet, you can't use update to create it. As its name implies, update can only be used to update an existing document.

To create a new document at a location you control, use set:

meetingRef.set(hashMapOf("users" to FieldValue.arrayUnion(userData)))

Also see the Firebase documentation on setting a document.

answered Nov 13, 2021 at 23:39

Frank van Puffelen

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2 Comments

cjames Over a year ago

Whoops. That definitely was it. facepalm I should have caught that for sure!

Shvet Over a year ago

I was trying add array from application side and tried many thing. Finally found solution here.

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