在 Firestore 中，如何更改某个字段具有某个值的集合的所有文档，该字段具有某个值？

Question

I want to change the value of a certain field of all documents in a Cloud Firestore collection to a certain value if that field is equal to a certain value. How do I do that?

Answer 1

1. Query with a filter that matches all of the documents you want to chage.
2. Iterate the results of that query.
3. Update each document with the new field value it should contain.

Answer 2

In addition to Doug's answer, if you want to update all documents in a collection where a field contains a certain value, then please use the following lines of code:

FirebaseFirestore db = FirebaseFirestore.getInstance();
Query query = db.collection("collName").whereEqualTo("fieldName", "fieldValue");
query.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<QuerySnapshot> task) {
        if (task.isSuccessful()) {
            for (DocumentSnapshot document : task.getResult()) {
                document.getReference().update("fieldToUpdate", "value");
            }
        }
    }
});