javascript - 如何对包含 equalTo() api 的 firebase 查询进行分页

Question

我正在使用 Firebase 编写一个购物网站。我在边栏中有一些类别和子类别，单击它们时，帖子提要应相应更新，按时间排序并仅显示所选类别的帖子。

在 firebase 数据库上发布对象:

    -KiKGQUZ4XaZPHxvOZD-addclose {
      categorie:0
      subCat: 2
      ....
    }

有很多帖子，我需要对它们进行分页

要做到这一点，我应该这样查询:

  dbRef
    .orderByChild('categories')
    .equalTo(category)
    .limitToLast(QUERY.PAGINATION_COUNT)
    .on('value', (snapshot) => {
      cb(_toArray(snapshot).reverse());
    });

但我不能使用 equalTo() 进行分页。

我认为解决方案应该是:

  dbRef
    .orderByChild('categories')
    .equalTo(category)
    .startAt(lastFetchedItem.fbKey)
    .limitToLast(QUERY.PAGINATION_COUNT)
    .on('value', (snapshot) => {
      cb(_toArray(snapshot).reverse());
    });

但是使用 firebase 不可能同时执行 equalTo 查询和 startAt

我该如何解决？

Answer 1

基于 this source看起来这个功能是不可能的，也不会被添加。不过你可以做这样的事情

1. 使用equalTo查询你的初始分页数量
2. 按以最后一个可见键结尾的键查​​询，如果类别与您想要的匹配，则过滤结果然后添加它，否则忽略它。

我用 Swift3 编写代码，但遇到了同样的问题，也许我的代码对其他人有帮助。

static func filterTableByCategory(tableNumber: String, category: String) {
        filteringRef.child(tableNumber).queryOrdered(byChild: "category").queryEqual(toValue: category).queryLimited(toLast: 9).observeSingleEvent(of: .value, with: { snap in

            if snap.exists() {
                currentTablePosts.removeAll()
                for child in snap.children {
                    let child = child as? DataSnapshot
                    if let post = child?.value as? [String: AnyObject] {
                        let posst = Post()
                        if let author = post["author"] as? String, let likes = post["likes"] as? Int, let pathToImage = post["pathToImage"] as? String, let postID = post["postID"] as? String, let postDescription = post["postDescription"] as? String, let timestamp = post["timestamp"] as? Double, let category = post["category"] as? String, let table = post["group"] as? String, let userID = post["userID"] as? String, let numberOfComments = post["numberOfComments"] as? Int, let region = post["region"] as? String {

                            posst.author = author
                            posst.likes = likes
                            posst.pathToImage = pathToImage
                            posst.postID = postID
                            posst.userID = userID
                            posst.fancyPostDescription = Helper.createAttributedString(author: author, postText: postDescription)
                            posst.postDescription = author + ": " + postDescription
                            posst.timestamp = timestamp
                            posst.table = table
                            posst.region = region
                            posst.category = category
                            posst.numberOfComments = numberOfComments
                            posst.userWhoPostedLabel = Helper.createAttributedPostLabel(username: author, table: table, region: region, category: category)

                            if let people = post["peopleWhoLike"] as? [String: AnyObject] {
                                for(_, person) in people {
                                    posst.peopleWhoLike.append(person as! String)
                                }
                            }
                            currentTablePosts.insert(posst, at: 0)
                            NotificationCenter.default.post(name: NSNotification.Name(rawValue: "reloadTableCollectionView"), object: nil)
                        } // end of if let
                    }
                }
            }
            else {
                currentTablePosts.removeAll()
                NotificationCenter.default.post(name: NSNotification.Name(rawValue: "reloadTableCollectionView"), object: nil)
            }
        })
        filteringRef.removeAllObservers()
    }

    static func getMoreFilterByCategoryPosts(tableNumber: String, category: String, lastVisibleKey: String) {

        pagingReference.child(tableNumber).queryOrderedByKey().queryEnding(atValue: lastVisibleKey).queryLimited(toLast: 12).observeSingleEvent(of: .value, with: { snap in

            if snap.exists() {
                let currentNumberOfPosts = currentTablePosts.count
                for child in snap.children {
                    let child = child as? DataSnapshot
                    if let post = child?.value as? [String: AnyObject] {
                        if let cat = post["category"] as? String, let postID = post["postID"] as? String {
                            if cat == category && postID != lastVisibleKey {
                                let posst = Post()
                                if let author = post["author"] as? String, let likes = post["likes"] as? Int, let pathToImage = post["pathToImage"] as? String, let postDescription = post["postDescription"] as? String, let timestamp = post["timestamp"] as? Double, let table = post["group"] as? String, let userID = post["userID"] as? String, let numberOfComments = post["numberOfComments"] as? Int, let region = post["region"] as? String {

                                    posst.author = author
                                    posst.likes = likes
                                    posst.pathToImage = pathToImage
                                    posst.postID = postID
                                    posst.userID = userID
                                    posst.fancyPostDescription = Helper.createAttributedString(author: author, postText: postDescription)
                                    posst.postDescription = author + ": " + postDescription
                                    posst.timestamp = timestamp
                                    posst.table = table
                                    posst.region = region
                                    posst.category = cat
                                    posst.numberOfComments = numberOfComments
                                    posst.userWhoPostedLabel = Helper.createAttributedPostLabel(username: author, table: table, region: region, category: category)

                                    if let people = post["peopleWhoLike"] as? [String: AnyObject] {
                                        for(_, person) in people {
                                            posst.peopleWhoLike.append(person as! String)
                                        }
                                    }
                                    currentTablePosts.insert(posst, at: currentNumberOfPosts)
                                    NotificationCenter.default.post(name: NSNotification.Name(rawValue: "reloadTableCollectionView"), object: nil)
                                } // end of if let
                            }
                        }
                    }
                }
            }
            else {
                print("snap == nil")
            }

        })
        pagingReference.removeAllObservers()

    }