从 Firebase RT 数据库中提取数据时遇到问题

Question

对编码非常陌生，如果这里有什么特别明显的地方，我们深表歉意。

我正在开发一个应用程序，可以用来跟踪我的举重训练。我这样写数据：

public func writeNewExercise(splitName: String, day: Int, exerciseNum: Int, exerciseName: String, sets: String, repsSecs: String, isTimed: Bool, completion: @escaping (Bool) -> Void) {
        
        let user = AuthManager.shared.user
        var exerciseRef: DatabaseReference!
        exerciseRef = Database.database().reference(withPath: "\(user.uid)/splits/\(splitName)/day \(day)/exercise \(exerciseNum)")
        
        var dataDictionary: [String: Any] = [:]
        dataDictionary["Exercise Name"] = exerciseName
        dataDictionary["Sets"] = sets
        dataDictionary["Reps or Secs"] = repsSecs
        dataDictionary["Is Timed"] = isTimed
        
        exerciseRef.setValue(dataDictionary) { error, _ in
            if error == nil {
                completion(true)
                return
            } else {
                completion(false)
                return
            }
            
        }
        
    }

这给了我一个 Firebase 中的 JSON 字典，如下所示：

{
  "8aIzPgurRLPPEYDpXWv54r5JjvH3" : {
    "splits" : {
      "Test Split" : {
        "day 1" : {
          "exercise 0" : {
            "Exercise Name" : "Curls",
            "Is Timed" : false,
            "Reps or Secs" : "12",
            "Sets" : "4"
          }
        }
      }
    }
  },

我现在要做的是提取这些数据，以便我可以将每个练习插入到 tableView 单元格中。不想对它做任何花哨的事情——只是能够查看它，这样我就可以跟随我的分裂。我这样做更多是为了练习而不是实用。我尝试了 15 种不同的方式提取数据，但无论我做什么都行不通。我完全被难住了。这是我现在的代码：

    public func downloadPost(splitName: String, day: Int, completion: @escaping (Bool) -> Void){
        
        let user = AuthManager.shared.user
        var exerciseRef: DatabaseReference!
        exerciseRef = Database.database().reference()
        
        var exerciseArray = [Exercise]()
        
        exerciseRef.child("Users").child(user.uid).child("splits").child(splitName).child("day \(day)").observe(.value) { snapshot in
            
            if snapshot.exists(){
                for x in 0...100{
                
                let nameValue = snapshot.childSnapshot(forPath: "exercise \(x)/Exercise Name").value
                let setsValue = snapshot.childSnapshot(forPath: "exercise \(x)/Sets").value
                let repsOrSecsValue = snapshot.childSnapshot(forPath: "exercise \(x)//Sets/Reps or Secs").value
                let isTimedValue = snapshot.childSnapshot(forPath: "exercise \(x)/Sets/Is Timed").value
                
                let exercise = Exercise(name: "\(nameValue!)",
                                        sets: "\(setsValue!)",
                                        repsOrSecs: "\(repsOrSecsValue!)",
                                        isTimed: isTimedValue as? Bool ?? false)
                    print(exercise.name)
                    print(exercise.sets)
                    print(exercise.repsOrSecs)
                    print(exercise.isTimed)
                exerciseArray.append(exercise)
                completion(true)
                return
            }
        } else {
            print("no snapshot exists")
        }
        
        print(exerciseArray)
        
    }
    }

Exercise 是我创建的一个自定义类，它有一个名称、组数、代表数和一个布尔“isTimed”。此代码打印：

不存在快照，[]

尝试其他的东西，我已经得到它来打印类似的东西：

空， 0, 0, 假的

我尝试过的其他一些东西是：

• 使用斜线导航而不是在 .observe.value 中链接 .childs
• 使用 .getData 代替 .observe
• 到处乱扔 DispatchQueue.main.async
• 将executiveRef设为整个数据库，然后在分配snapshot.value时调用到特定点
• 还有很多

此时我可能已经为此投入了大约 15 个小时，但我真的无法弄清楚。任何帮助将不胜感激。如果需要，我会密切关注这篇文章并发布我可能遗漏的任何信息。

谢谢！

更新

使用下面 Medo 提供的代码，一切正常。对于其他尝试做这样的事情的人，在像 Medo 演示的那样拉数组之后，只需将 tableViewCell 中的所有标签设置为 ExportedArray[indexPath.row].theClassPropertyYouWant

Answer 1

这是我的解决方案：

public func downloadPost(splitName: String, day: Int, completion: @escaping (([Exercise]) -> ())){
    
    let user = AuthManager.shared.user
    var exerciseRef: DatabaseReference!
    exerciseRef = Database.database().reference()
    
    var exerciseArray = [Exercise]()
    
    exerciseRef.child(user.uid).child("splits").child(splitName).child("day \(day)").observe(.value, with: { snapshot in
        
        guard let exercises = snapshot.children.allObjects as? [DataSnapshot] else {
            print("Error: No snapshot")
            return
        }
        
        
        
        for exercise in exercises {
            let exerciseData = exercise.value as? [String:Any]
            
            let exerciseName = exerciseData["Exercise Name"] as? String
            let isTimed = exerciseData["Is Timed"] as? Bool
            let repsOrSecs = exerciseData["Reps or Secs"] as? String
            let sets = exerciseData["Sets"] as? String
            
            let exerciseIndex = Exercise(name: "\(exerciseName)",
                                    sets: "\(sets)",
                                    repsOrSecs: "\(repsOrSecs)",
                                    isTimed: isTimed)
            
            exerciseArray.append(exerciseIndex)
            
        }
      completion(exerciseArray)  
    }
}

您可以像这样调用函数downloadPost 并从中提取数组：

downloadPost(splitName: "", day: 0, completion: {
    aNewArray in
    
    // aNewArray is your extracted array [Exercise]
    print("\(aNewArray)")
    
})

需要注意的几件事：

1. 如果您想确保按顺序存储练习（并按顺序提取数据），那么不要将练习 0、1、2...（在您的数据库中）命名为“childByAutoId” ”。 Firebase 会在您添加/推送或提取数据时自动为您排序。将您的 writeNewExercise 函数替换为：

   let user = AuthManager.shared.user
   var exerciseRef: DatabaseReference!
   let key = Database.database().reference().childByAutoId().key ?? ""
   exerciseRef = Database.database().reference(withPath: "\(user.uid)/splits/\(splitName)/day \(day)/\(key)")
   
   var dataDictionary: [String: Any] = [:]
   dataDictionary["Exercise Name"] = exerciseName
   dataDictionary["Sets"] = sets
   dataDictionary["Reps or Secs"] = repsSecs
   dataDictionary["Is Timed"] = isTimed
   
   exerciseRef.setValue(dataDictionary) { error, _ in
       if error == nil {
           completion(true)
           return
       } else {
           completion(false)
           return
       }
   
   }
   

2. Firebase 实时数据库是一种广度优先搜索和下载。所以你应该尽可能地扁平化你的数据库结构。这意味着在exerciseRef.child("Users").child(user.uid).child("splits").child(splitName).child("day \(day)") 上观察仍然会下载所有练习日。