我正在用firebase编写一个购物网站。 我在侧边栏中有一些类别和子类别，点击它们，帖子提要应相应更新，按时间排序，只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());
});
但我不能用equalTo（）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firebase不能同时执行equalTo查询和startAt
如何解决？
答案 0 :(得分：0)
基于this source，看起来这个功能是不可能的，不会被添加。你可以做这样的事情
我在Swift3中编写了我的代码，但遇到了同样的问题，也许我的代码会对其他人有所帮助。
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()
}
答案 1 :(得分：0)
我最终改变了firebase实时数据库架构。
我不确定，但我认为firebase故意不释放更多api。它迫使你仔细检查你的架构并改进它。
我为类别创建了一个专用集合，并在类别集合中为每个类别创建了单独的节点。 它是构建数据库的firebase recommend。
然后将每个新帖子放入相应的类别。
因此，我可以轻松地在每个类别和子类别中使用OrderByKey()，并使用startAt或endAt apis
另一种解决方案是使用firebase功能和弹性搜索。 为此目的创建了FlashLight package。