Firebase - 如果设置为分页的键已被删除，如何处理分页

我使用这个问题底部的分页方法，效果很好。一旦startKey使用keyfrom初始化，db下一个分页将发生，下一组帖子（子级）将附加到数据源。

我意识到，如果它key被发布它的初始用户删除，那么一旦我尝试从中分页，key因为它不存在，如果它存在就会被附加的孩子不会被附加，因为他们不会可访问（它们可基于该密钥访问）。

The only thing I could think of was to first check if the key exists() and if it doesn't just start everything over from the beginning:

if !snapshot.exists() {

     self?.startKey = nil
     self?.datasource.removeAll()
     self?.collectionView.reloadData()
     self?.handlePagination()                    
     return
 }

It works fine but it's not the most fluid user experience because I'd rather just pull the posts prior to the deleted key (I have no prior reference to them).

A possibility is to just keep an array of all the previous keys and just loop through them but there's always a minute chance that those keys can get deleted by the users who posted them also.

Any ideas of how to get around this?

var startKey: String?

func handlePagination() {

    if startKey == nil {

        Database...Ref.child("posts")
          .queryOrderedByKey()
          .queryLimited(toLast: 7)
          .observeSingleEvent(of: .value, with: { [weak self](snapshot) in

            guard let children = snapshot.children.allObjects.first as? DataSnapshot else { return}

            for child in snapshot.children.allObjects as! [DataSnapshot] {
                    // append child to datasource
            }
            self?.startKey = children.key
        })

    } else {

        Database...Ref.child("posts")
          .queryOrderedByKey()
          .queryEnding(atValue: startKey!)
          .queryLimited(toLast: 8)
          .observeSingleEvent(of: .value, with: { [weak self](snapshot) in

            if !snapshot.exists() {

                self?.startKey = nil
                self?.datasource.removeAll()
                self?.collectionView.reloadData()
                self?.handlePagination()                    
                return
            }

            guard let children = snapshot.children.allObjects.first as? DataSnapshot else { return}

            for child in snapshot.children.allObjects as! [DataSnapshot] {
                // insert child in datasource at startIndex
            }
            self?.startKey = children.key
        })
    }
}