How to Delete Firestore Collections and Subcollections Without Restructuring?

Deleting Collections and Subcollections in Firestore

Firestore provides a hierarchical data structure with collections and documents. Collections can hold subcollections, creating a multi-level nesting. When deleting a specific list, the challenge arises due to the inability to delete a list ID while preserving its subcollections.

Solution Without Restructuring:

To bypass this issue, the following steps can be used:

1. Retrieve all documents within the employees subcollection and delete them.
2. Retrieve all documents within the locations subcollection and delete them.
3. Delete the listId document.

This approach ensures the complete removal of the list and associated data without compromising the structure of the database.

Considerations for Large Collections:

When dealing with large collections, it's recommended to delete documents in smaller batches to mitigate potential out-of-memory errors. The deletion process should continue until all documents within the collection or subcollection have been removed.

Caution Regarding Delete Operations:

While the delete operation is technically possible, the Firebase team strongly discourages its use due to potential security and performance implications. It's only advised for deleting small collections, especially when performed from a trusted server environment.

Android Implementation:

For Android applications, the following code snippet can be employed to 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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