How to Delete Firestore Collections and Subcollections Effectively?

Deleting Collections and Subcollections in Firestore

Problem Statement:

In a Firestore database with a collection of lists, each list contains two subcollections: employees and locations. When a user wishes to delete a specific list, deleting the list document alone does not remove the subcollections. This issue arises due to the Firestore documentation's indication that deleting a document with subcollections does not automatically remove those subcollections.

Proposed Solutions:

1. Delete Subcollections Iteratively:

• Retrieve all documents within the employees and locations subcollections.
• Delete each retrieved document.
• Delete the list document.

2. Use the deleteCollection Method (Not Recommended):

• The Firestore deleteCollection method deletes all documents within a collection recursively.
• Use this method only for small collections to avoid memory errors.
• Ensure to execute this operation from a trusted server environment.

Android Code for Recursive Deletion:

The following Android code demonstrates how to recursively delete a collection:

<code class="java">private void deleteCollection(final CollectionReference collection, Executor executor) {
    Tasks.call(executor, () -> {
        int batchSize = 10;
        Query query = collection.orderBy(FieldPath.documentId()).limit(batchSize);
        List<DocumentSnapshot> deleted = deleteQueryBatch(query);

        while (deleted.size() >= batchSize) {
            DocumentSnapshot last = deleted.get(deleted.size() - 1);
            query = collection.orderBy(FieldPath.documentId()).startAfter(last.getId()).limit(batchSize);

            deleted = deleteQueryBatch(query);
        }

        return null;
    });
}

@WorkerThread
private List<DocumentSnapshot> deleteQueryBatch(final Query query) throws Exception {
    QuerySnapshot querySnapshot = Tasks.await(query.get());

    WriteBatch batch = query.getFirestore().batch();
    for (DocumentSnapshot snapshot : querySnapshot) {
        batch.delete(snapshot.getReference());
    }
    Tasks.await(batch.commit());

    return querySnapshot.getDocuments();
}</code>

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