Firestore - Recursively Copy A Document And All It's Subcollections/documents

we're using Google's Firestore for embedded machine configuration data. Because this data controls a configurable pageflow and lots of other things, it's segmented up into lots of

Solution 1:

You can use something like this to recursively read and write from a collection to another one:

defread_recursive(
    source: firestore.CollectionReference,
    target: firestore.CollectionReference,
    batch: firestore.WriteBatch,
) -> None:
    global batch_nr

    for source_doc_ref in source:
        document_data = source_doc_ref.get().to_dict()
        target_doc_ref = target.document(source_doc_ref.id)
        if batch_nr == 500:
            log.info("commiting %s batched operations..." % batch_nr)
            batch.commit()
            batch_nr = 0
        batch.set(
            reference=target_doc_ref,
            document_data=document_data,
            merge=False,
        )
        batch_nr += 1for source_coll_ref in source_doc_ref.collections():
            target_coll_ref = target_doc_ref.collection(source_coll_ref.id)
            read_recursive(
                source=source_coll_ref.list_documents(),
                target=target_coll_ref,
                batch=batch,
            )

batch = db_client.batch()
read_recursive(
    source=db_client.collection("src_collection_name"), 
    target=db_client.collection("target_collection_name"), 
    batch=batch,
)
batch.commit()

Writes are in batches and this saves a lot of time (in my case it finished in half the time compared with set).