Kotlin + Firestore: How to add field to certain data of firestore database?

Question

I add data to firestore with below code.

        val user = hashMapOf(
            "loginType" to "app",
            "userId" to auth.currentUser,
            "createdTime" to current_time,
            "name" to (binding.nameInput.text.toString()),
            "gender" to (binding.genderInput.selectedItem.toString()),
            "phone" to phoneNumber,
            "birth" to (birthDBInput),
            "community" to (binding.communityInput.selectedItem.toString())
        )

        db.collection("users")
            .add(user)
            .addOnSuccessListener {
                startActivity(Intent(this@RegisterActivity, DiaryActivity::class.java))
            }

And this make data structure in firestore as below.

Here, I want to add one more field named 'community' to one data which has certain userId in this other component.

So I tried to write some code like below.

    var communityMap = hashMapOf<String, String>(
        "community" to binding.communityInput.toString()
    )

    binding.registerBtn.setOnClickListener {
    db.collection("users").whereEqualTo("userId", userId)
        .update(communityMap as Map<String, Any>)
        .addOnSuccessListener {
            startActivity(Intent(this@CommunityRegisterActivity, DiaryActivity::class.java))
        }

But update function doesn't work (It says this function doesn't exist) And set is also same not working.

For this purpose, How can I extract certain data and add field?

Answer 1

Firestore doesn't support so-called update queries, where you send the query conditions and an update instruction to the database. Instead you will have to execute the query in your application code, read the results, and then update each individual resulting document.

Something like:

db.collection("users").whereEqualTo("userId", userId)
    .get()
    .addOnSuccessListener { documents ->
        for (document in documents) {
            document.reference.update(communityMap as Map<String, Any>)
        }
    }