iOS Firebase - 向下查询多个级别的最佳方式是什么？ 'InvalidQueryParameter' , 原因 : 'Cannot use multiple queryOrderedBy calls!'

Question

我正在使用 UISearchController 并且我想在注释键上查询从根向下的 2 个节点。它将是 root > posts > uid > postId > comment

root
  |
  @--posts
       |
       @--uid123
            |
            @--postId987
                  |
                  |-comment: "I like pizza"

我尝试链接多个查询 let commentRef = postsRef.queryOrderedByKey().queryOrdered(byChild: "comment").queryStarting(atValue: searchText).queryEnding(atValue: searchText+"\u{f8ff}" 但我遇到了崩溃:

*** Terminating app due to uncaught exception 'InvalidQueryParameter', reason: 'Cannot use multiple queryOrderedBy calls!'

向下查询多个级别的最佳方式是什么？

导致崩溃的代码:

func updateSearchResults(for searchController: UISearchController) {

    guard let searchText = searchController.searchBar.text?.lowercased() else { return }

    let postsRef = Database.database().reference().child("posts")

    let commentRef = postsRef.queryOrderedByKey().queryOrdered(byChild: "comment").queryStarting(atValue: searchText).queryEnding(atValue: searchText+"\u{f8ff}")

    commentRef.observeSingleEvent(of: .value, with: { (snapshot) in

        guard let dictionaries = snapshot.value as? [String: Any] else { return }

        dictionaries.forEach({ (key, value) in

            guard let dict = value as? [String: Any] else { return }
            let post = Post(dict: dict)

            let isContained = self.filteredComments.contains(where: { (containedPost) -> Bool in
                return post.comment == containedPost.comment
            })
            if !isContained {
                self.filteredComments.append(post)
                self.collectionView?.reloadData()
            }
        })
    })
}

我在下面找到了另一种方法。我首先在 posts ref 上获取 .value，遍历所有子项，然后将每个 snapshot.key 作为子项附加到 postsRef 并从那里获取评论.它确实有效。问题是它似乎效率不高，尤其是当有数百万的帖子和/或用户需要整理时。

let postsRef = Database.database().reference().child("posts")

postsRef.observeSingleEvent(of: .value) { (snapshot) in

    for child in snapshot.children {

        let uid = child as! DataSnapshot

        let commentRef = postsRef.child(uid.key).queryOrdered(byChild: "comment").queryStarting(atValue: searchText).queryEnding(atValue: searchText+"\u{f8ff}")

        commentRef.observeSingleEvent(of: .value, with: { (snapshot) in
            // the rest of the code
    }

Answer 1

我将把它作为一个可能的解决方案抛出。

目前的结构为何如此还不是很清楚，但我建议将其更改为

post_comments
   post_id_x
      posted_by: "uid1234"
      comment: "I like pizza"

如果结构需要保持原样，那么只需将其添加为另一个节点，这将使您的评论查询更加简单。