Firebase 数据库索引路径答案

【问题标题】：Firebase Database indexPathFirebase 数据库索引路径
【发布时间】：2017-08-20 01:08:31
【问题描述】：

我正在尝试使用此函数从 firebase 检索数据，但我没有获得所有数据：

 func retrieveVideos(_ completionBlock: @escaping (_ success: Bool, _ error: Error?) -> ()) {
    let userMessagesRef = DataService.instance.REF_ARTISTARTS.child(Auth.auth().currentUser!.uid)

    userMessagesRef.observe(.childAdded, with: { [weak self] (snapshot) in

        if let snapshot = snapshot.children.allObjects as? [DataSnapshot] {

print("SNAPSHOT: (snapshot.count)") = 12

        }
        guard let strongSelf = self else {return}

        guard let dictionary = snapshot.value as? [String: AnyObject] else {
            completionBlock(false, nil)
            return
        }
        var arts = [Art?]()
        if let art = ArtViewModelController.parse(dictionary) {
            arts.append(art)

            print(arts.count) = 1

        }
        strongSelf.viewModels = ArtViewModelController.initViewModels(arts)
        completionBlock(true, nil)

    }) { (error: Error) in
        completionBlock(false, error)
    }
}



var viewModelsCount: Int {
    return viewModels.count
}


func viewModel(at index: Int) -> ArtViewModel? {
    guard index <= 0 && index < viewModelsCount else { return nil }
    return viewModels[index]
}

}

private extension ArtViewModelController {

static func parse(_ dictionary: [String: Any]) -> Art? {
    let artID = dictionary["artID"] as? String ?? ""
    let imgUrl = dictionary["imageUrl"] as? String ?? ""
    let title = dictionary["title"] as? String ?? ""
    let description = dictionary["description"] as? String ?? ""
    let price = dictionary["price"] as? NSNumber ?? 0
    let type = dictionary["type"] as? String ?? ""
    let height = dictionary["height"] as? NSNumber ?? 0
    let width = dictionary["width"] as? NSNumber ?? 0
    let postDate = dictionary["postDate"] as? NSNumber ?? 0
    return Art(artID: artID, imgUrl: imgUrl, price: price, title: title, description: description, type: type, height: height, width: width, postDate: postDate)
}


static func initViewModels(_ arts: [Art?]) -> [ArtViewModel?] {
    print("SECOND VIDEO COUNT: \(arts.count)")
    return arts.map { art in
        if let art = art {
            return ArtViewModel(art: art)
        } else {
            return nil
        }
    }
}

}

我的问题是我的 index.count 总是等于 1 但它应该等于 12。

这是原始代码：

 func retrieveUsers(_ completionBlock: @escaping (_ success: Bool, _ error: NSError?) -> ()) {
    let urlString = "http://localhost:3000/users"
    let session = URLSession.shared

    guard let url = URL(string: urlString) else {
        completionBlock(false, nil)
        return
    }
    let task = session.dataTask(with: url) { [weak self] (data, response, error) in
        guard let strongSelf = self else { return }
        guard let data = data else {
            completionBlock(false, error as NSError?)
            return
        }
        let error = NSError.createError(0, description: "JSON parsing error")
        if let jsonData = try? JSONSerialization.jsonObject(with: data, options: .allowFragments) as? [[String: AnyObject]] {
            guard let jsonData = jsonData else {
                completionBlock(false,  error)
                return
            }
            var users = [User?]()
            for json in jsonData {
                if let user = UserViewModelController.parse(json) {
                    users.append(user)
                }
            }

            strongSelf.viewModels = UserViewModelController.initViewModels(users)
            completionBlock(true, nil)
        } else {
            completionBlock(false, error)
        }
    }
    task.resume()
}

所以我正在尝试使用 Firebase 做同样的事情。如果您需要更多详细信息，请询问！

快照打印：

    SNAPSHOT: Optional({
    description = "Yes ";
    height = 87;
    imageUrl = "https://firebasestorage.googleapis.com/v0/b/medici-b6f69.appspot.com/o/Art%2F4bjurh5FFNOUb2D4oHGfRqEm7Il2%2FB6E2A9F0-C409-4732-B6D9-14382E6796F5?alt=media&token=32992b9c-4a08-456d-8950-119f681b4cdc";
    postDate = 1498921599547;
    price = 23;
    private = 0;
    title = "Yes ";
    type = Modern;
    userUID = 4bjurh5FFNOUb2D4oHGfRqEm7Il2;
    width = 71;
})
SNAPSHOT: Optional({
    artHeight = 85;
    artWidth = 123;
    description = "Yes ";
    height = 85;
    imageUrl = "https://firebasestorage.googleapis.com/v0/b/medici-b6f69.appspot.com/o/Art%2F4bjurh5FFNOUb2D4oHGfRqEm7Il2%2F16280189-5AEA-47CB-9251-C95635FFE56C?alt=media&token=8198df4e-da8c-4883-b278-fc7c14730f69";
    postDate = 1498921623601;
    price = 23;
    private = 0;
    title = "blacks don\U2019t Crack ";
    type = Abstract;
    userUID = 4bjurh5FFNOUb2D4oHGfRqEm7Il2;
    width = 123;
})
SNAPSHOT: Optional({
    artHeight = 81;
    artWidth = 11;
    description = "Yes ";
    height = 81;
    imageUrl = "https://firebasestorage.googleapis.com/v0/b/medici-b6f69.appspot.com/o/Art%2F4bjurh5FFNOUb2D4oHGfRqEm7Il2%2F305FDE5C-1C5C-4ABD-B4A1-4FA224421202?alt=media&token=fcba57df-e252-47c2-be92-7836bd97e6fe";
    postDate = 1502242913081;
    price = 23;
    private = 0;
    title = "Title ";
    type = type;
    userUID = 4bjurh5FFNOUb2D4oHGfRqEm7Il2;
    width = 118;
})
SNAPSHOT: Optional({
    description = "Hey ";
    height = 82;
    imageUrl = "https://firebasestorage.googleapis.com/v0/b/medici-b6f69.appspot.com/o/Art%2F4bjurh5FFNOUb2D4oHGfRqEm7Il2%2F04B00727-2AE4-41E3-BCA3-3980182C7F67?alt=media&token=cc1d6a92-1625-453c-bf1f-2ec84d6df51a";
    postDate = 1503341277594;
    price = 23;
    private = 0;
    title = "Title ";
    type = Modern;
    userUID = 4bjurh5FFNOUb2D4oHGfRqEm7Il2;
    width = 124;
})




   DIC: ["height": 87, "private": 0, "width": 71, "postDate": 1498921599547, "description": Yes , "title": Yes , "imageUrl": https://firebasestorage.googleapis.com/v0/b/medici-b6f69.appspot.com/o/Art%2F4bjurh5FFNOUb2D4oHGfRqEm7Il2%2FB6E2A9F0-C409-4732-B6D9-14382E6796F5?alt=media&token=32992b9c-4a08-456d-8950-119f681b4cdc, "userUID": 4bjurh5FFNOUb2D4oHGfRqEm7Il2, "price": 23, "type": Modern]
DIC: ["artWidth": 123, "height": 85, "private": 0, "artHeight": 85, "description": Yes , "postDate": 1498921623601, "width": 123, "imageUrl": https://firebasestorage.googleapis.com/v0/b/medici-b6f69.appspot.com/o/Art%2F4bjurh5FFNOUb2D4oHGfRqEm7Il2%2F16280189-5AEA-47CB-9251-C95635FFE56C?alt=media&token=8198df4e-da8c-4883-b278-fc7c14730f69, "title": blacks don’t Crack , "price": 23, "type": Abstract, "userUID": 4bjurh5FFNOUb2D4oHGfRqEm7Il2]
DIC: ["artWidth": 11, "height": 81, "private": 0, "artHeight": 81, "description": Yes , "postDate": 1502242913081, "width": 118, "imageUrl": https://firebasestorage.googleapis.com/v0/b/medici-b6f69.appspot.com/o/Art%2F4bjurh5FFNOUb2D4oHGfRqEm7Il2%2F305FDE5C-1C5C-4ABD-B4A1-4FA224421202?alt=media&token=fcba57df-e252-47c2-be92-7836bd97e6fe, "title": Title , "price": 23, "type": type, "userUID": 4bjurh5FFNOUb2D4oHGfRqEm7Il2]
DIC: ["height": 82, "private": 0, "width": 124, "postDate": 1503341277594, "description": Hey , "title": Title , "imageUrl": https://firebasestorage.googleapis.com/v0/b/medici-b6f69.appspot.com/o/Art%2F4bjurh5FFNOUb2D4oHGfRqEm7Il2%2F04B00727-2AE4-41E3-BCA3-3980182C7F67?alt=media&token=cc1d6a92-1625-453c-bf1f-2ec84d6df51a, "userUID": 4bjurh5FFNOUb2D4oHGfRqEm7Il2, "price": 23, "type": Modern]

【问题讨论】：

您可以尝试断点调试，并使用po OBJECTNAME 打印对象，看看哪一行可能不起作用？
请添加打印（快照）然后你能显示它打印的内容吗？
你的问题解决了吗？
@user1000 不，我还在努力。
您检查过我的答案并相应地更新了代码吗？

标签： ios swift firebase firebase-realtime-database

【解决方案1】：

能否在调用ArtViewModelController.parse(dictionary)之前附上print(dictionary)和print(snapshot.value)的输出？

var arts = [Art?]()
print(dictionary)      // -> output #1
print(snapshot.value)  // -> output #2
if let art = ArtViewModelController.parse(dictionary) {
    arts.append(art)
[...]

【讨论】：

谢谢，我只是用打印件编辑我的问题。所有数据都在打印中
问题出在这一行： if let art = ArtViewModelController.parse(dictionary) 。我知道问题出在哪里，但无法解决。
谢谢@John！您的输出显示您已经检索了 DataSnapshot 的数组： Optional({ description = "Yes "; [...[]] width = 71; }) 此时，最简单的解决方案是遍历它们并，而不是使用 parse 方法，只需从每个 DataSnapshot 项目初始化您的 Art 实例。
谢谢@Andrea P，请给我一个例子。我是新来的。非常感谢。

【解决方案2】：

您可以尝试以下两个选项。

选项#1

这应该与 snapshot.value 返回完整字典（12 个项目的数组）的假设一起工作：

func retrieveVideos(_ completionBlock: @escaping (_ success: Bool, _ error: Error?) -> ()) {
    let userMessagesRef = DataService.instance.REF_ARTISTARTS.child(Auth.auth().currentUser!.uid)

    userMessagesRef.observe(.childAdded, with: { [weak self] (snapshot) in
        guard let dictionary = snapshot.value as? [String: AnyObject] else {
            completionBlock(false, nil)
            return
        }
        guard let strongSelf = self else {return}

        var arts = [Art?]()
        if let art = ArtViewModelController.parse(dictionary) {
            arts.append(art)
        }
        strongSelf.viewModels = ArtViewModelController.initViewModels(arts)
        completionBlock(true, nil)

    }) { (error: Error) in
        completionBlock(false, error)
    }
}

选项 #2

如果可行，选项 #1 是更简单的解决方案。否则，由于每个DataSnapshot 的内容看起来都是一个字典，所以下面的代码可能会起作用：

func retrieveVideos(_ completionBlock: @escaping (_ success: Bool, _ error: Error?) -> ()) {
   let userMessagesRef = DataService.instance.REF_ARTISTARTS.child(Auth.auth().currentUser!.uid)

   userMessagesRef.observe(.childAdded, with: { [weak self] (snapshot) in
      guard let strongSelf = self else {return}
      var arts = [Art?]()
      for snapshotItem in snapshot.children.allObjects as? Dictionary {
          let art = Art(snapshot: snapshotItem)
          arts.append(art)
      }
      strongSelf.viewModels = ArtViewModelController.initViewModels(arts)
      completionBlock(true, nil)
   }
}) { (error: Error) in
    completionBlock(false, error)
}

您应该将Art(snapshot: Dictionary) 添加到Art 类中：

// Initialize Art from dictionary
func Art(snapshot: Dictionary) {
    let artID = dictionary["userUID"] as? String ?? ""
    let imgUrl = dictionary["imageUrl"] as? String ?? ""
    let title = dictionary["title"] as? String ?? ""
    let description = dictionary["description"] as? String ?? ""
    let price = dictionary["price"] as? NSNumber ?? 0
    let type = dictionary["type"] as? String ?? ""
    let height = dictionary["artHeight"] as? NSNumber ?? 0
    let width = dictionary["artWidth"] as? NSNumber ?? 0
    let postDate = dictionary["postDate"] as? NSNumber ?? 0
    return Art(artID: artID, imgUrl: imgUrl, price: price, title: title, description: description, type: type, height: height, width: width, postDate: postDate)
}

注意：我假设您在 DataSnapshot 中查找的密钥是 userUID，因为我没有看到 artID（在解析代码中）。

【讨论】：

【解决方案3】：

使用这个：-

func retrieveVideos(_ completionBlock: @escaping (_ success: Bool, _ error: Error?) -> ()) {
let userMessagesRef = DataService.instance.REF_ARTISTARTS.child(Auth.auth().currentUser!.uid)

userMessagesRef.observe(.value, with: { [weak self] (snapshot) in

    if let snapshots = snapshot.children.allObjects as? [DataSnapshot] 
       {
        print("SNAPSHOT: (snapshots.count)")
         }


      var arts = [Art]()


     guard let strongSelf = self else {return}

    for snapshot in snapshots {
        let dictionary = snapshot.value as? [String: AnyObject]

        if let art = ArtViewModelController.parse(dictionary) {
            arts.append(art)
        }
    }

    strongSelf.viewModels = ArtViewModelController.initViewModels(arts)
    completionBlock(true, nil)

}) { (error: Error) in
    completionBlock(false, error)

} }

【讨论】：