通过嵌套的Firebase数据循环填充数组Swift

本文介绍了通过嵌套的Firebase数据循环填充数组Swift的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我想通过从一个Firebase节点获取值来填充数组，并使用这些值从另一个Firebase节点获取信息.我该怎么办?

I want to fill an array by fetching values from one firebase node and use those values to fetch information from a different firebase node. How do I do that?

这是我的Firebase数据库的样子:

This is what my firebase database looks like:

{ "MainTree" : { "subTree1" : { "JiRtkpIFLVFNgmNBpMj" : { "PiRterKFLVFNgmFFFtu" : "PiRterKFLVFNgmFFFtu" "TfRterKFLVFNgmFGFre" : "TfRterKFLVFNgmFGFre", "X4RterKFLVFNgmaDFca" : "X4RterKFLVFNgmaDFca" } }, "subTree2" : { "PiRterKFLVFNgmFFFtu" : { "username" : "user1", "uid" : "PiRterKFLVFNgmFFFtu" }, "TfRterKFLVFNgmFGFre" : { "username" : "user2", "uid" : "TfRterKFLVFNgmFGFre" }, "X4RterKFLVFNgmaDFca" : { "username" : "user3", "uid" : "X4RterKFLVFNgmaDFca" } } } }

我的功能

func fetchAllInformation(uid: String, completion: @escaping ([UserData]) -> (), withCancel cancel: ((Error) -> ())?) { let ref = Database.database().reference().child("MainTree").child("subTree1").child(uid) ref.observeSingleEvent(of: .value, with: { (snapshot) in if snapshot.exists(){ guard let dictionaries = snapshot.value as? [String: Any] else { completion([]) return } var Values = [UserData]() let group = DispatchGroup() dictionaries.forEach({ (key, value) in group.enter() let ref = Database.database().reference().child("MainTree").child("subTree2").child(key) ref.observeSingleEvent(of: .value, with: { (snapshot) in guard let userDictionary2 = snapshot.value as? [String: Any] else { return } let user = UserData(dictionary: userDictionary2) Values.append(user) }) { (err) in print("Failed to fetch all user data from database:", (err)) cancel?(err) } }) group.notify(queue: .main) { print("loop done") completion(Values) } } }) { (err) in print("Failed to fetch all data from database:", (err)) cancel?(err) } }

我的通话功能:

fetchAllInformation(uid: "JiRtkpIFLVFNgmNBpMj", completion: { (userdata) in print("fetched all userdata! : ",userdata) }) { (err) in print("data fetch failed") }

我的数据结构

struct UserData { let uid: String let username: String init(dictionary: [String: Any]) { self.uid = dictionary["id"] as? String ?? "" self.username = dictionary["username"] as? String ?? "" } }

对异步代码可能是一种误解.现在的问题是数组变成空的.

It might be a misunderstanding with asynchronous code. Right now the problem is that the array is turning up empty.

推荐答案

我认为您要问的是如何遍历一系列节点，如何从该节点获取另一个节点的子键，然后从另一个节点读取数据这些键为基础的节点.

I think what's you're asking is how to iterate over a series of nodes, getting another nodes child keys from that node, then reading the data from the other node based on those keys.

让我从一个Firebase结构开始，该结构应该有助于阐明

Let me start with a Firebase structure that should help clarify

MainTree subTree1 some_node subTree2_0: true subTree2_1: true subTree2_2: true subTree2 subTree2_0: user_name: "Larry" subTree2_1: user_name: "Moe" subTree2_1: user_name: "Curly"

那应该符合问题的结构.

That should match up to the structure in the question.

我们将遍历MainTree/subTree1/some_node中的子节点，以获取要从subTree2中读取的节点.我不知道与其余数据有关的some_node是什么，所以我将其称为... some_node.

We're going to iterate over the child nodes located in MainTree/subTree1/some_node to get the nodes we want to read from subTree2. I didn't know what some_node was in respect to the rest of the data so I just called it... some_node.

第一部分代码立即读取subTree1节点的子节点，然后对其进行迭代以获取每个子键-该子键(例如subTree2_0)对应于subTree2中的一个子节点

This first section of code reads the subTree1 node child nodes at once, then iterates over them to get each child key - that child key (e.g. subTree2_0) corresponds to a child node in subTree2

func readMainTree() { let mainTreeRef = self.ref.child("MainTree") let subTree1Ref = mainTreeRef.child("subTree1") let someNodeRef = subTree1Ref.child("some_node") someNodeRef.observeSingleEvent(of: .value, with: { snapshot in let childNodes = snapshot.children.allObjects as! [DataSnapshot] for childSnap in childNodes { self.readSubTree2At(node: childSnap.key) } }) }

在for..loop内，我们获得每个子键，并将其传递给读取子数据(用户名)并打印出来的函数.

Within the for..loop, we get each child key and pass that to the function that reads the child data (user_name) and prints it out.

func readSubTree2At(node: String) { let mainTreeRef = self.ref.child("MainTree") let subTree2Ref = mainTreeRef.child("subTree2") let childRef = subTree2Ref.child(node) childRef.observeSingleEvent(of: .value, with: { snapshot in let userName = snapshot.childSnapshot(forPath: "user_name").value as? String ?? "No Name" print(userName) }) }

，输出为:

Larry Mo Curly

如果需要，可以将dispatchGroup放入混合中.这是使用DispatchGroup的解决方案

You could throw a dispatchGroup into the mix if you want.. here's a solution using a DispatchGroup

func readMainTreeWithDispatch() { let mainTreeRef = self.ref.child("MainTree") let subTree1Ref = mainTreeRef.child("subTree1") let someNodeRef = subTree1Ref.child("some_node") someNodeRef.observeSingleEvent(of: .value, with: { snapshot in let childNodes = snapshot.children.allObjects as! [DataSnapshot] let myGroup = DispatchGroup() for childSnap in childNodes { let mainTreeRef = self.ref.child("MainTree") let subTree2Ref = mainTreeRef.child("subTree2") let childRef = subTree2Ref.child(childSnap.key) myGroup.enter() childRef.observeSingleEvent(of: .value, with: { snapshot in let userName = snapshot.childSnapshot(forPath: "user_name").value as? String ?? "No Name" print(userName) myGroup.leave() }) } myGroup.notify(queue: .main) { print("Finished reading all user names.") } }) }

和输出

Larry Mo Curly Finished reading all user names.