For those who have deleted a document in Firestore but the subcollection does not disappear

I was trying to implement the posting function of SNS using Firebase / Firestore.

• We would appreciate it if you could point out any differences.

However, even though I deleted the posts (posts / {postId}), the sub-collection (comments / {comment} does not disappear ...

Sorry for the cluttered notation of document and subcollection.

I did a lot of research there, but ... ・ Delete using Cloud Fuctions -Write a method to fetch the comment document separately and delete it Only articles.

CloudFuctions seems to be deprecated because it is too slow.

So, as a result of careful consideration while looking at the Tutorial,

func delete(collection: CollectionReference, batchSize: Int = 100, completion: @escaping (Error?) -> ()) {
        collection.limit(to: batchSize).getDocuments { (docset, error) in
            
            guard let docset = docset else {
                completion(error)
                return
            }
            
            guard docset.count > 0 else {
                completion(nil)
                return
            }
            
            let batch = collection.firestore.batch()
            docset.documents.forEach {batch.deleteDocument($0.reference)}
            batch.commit { (batchError) in
                
                if let batchError = batchError {
                    completion(batchError)
                }
                else {
                    self.delete(collection: collection, batchSize: batchSize, completion: completion)
                }
            }
        }
    }

This function worked fine. Please apply the completion part according to what you want to make.

It's for my own memo, and I hope it helps because anyone can do it.