IOS Swift - 從Firebase數據庫中的不同節點獲取值

Question

我想要獲取事件參與者列表，在事件節點中，只列出員工的ID號。我想實現的是從員工節點獲取與該ID＃關聯的名稱。這是我的dbase的結構。

events: 
    uuid: 
     name: summer festival 2017 
     site: vegas 
     participants: 
      employeeID1: true 
      employeeID2: true 

Employee: 
    employeeID1: 
     name: gary 
     department: video production 

，這裏是我的代碼

@IBAction func downloadButtonAction(_ sender: UIButton) { 

     ref.child("events").child(eventKeyLabel.text!).child("participants").observeSingleEvent(of: .value, with: {(snapshot) in 

      // get the dictionary from the snapshot 
      if let participantsDict = snapshot.value as? [String : AnyObject] { 


       for each in participantsDict { 

        let employeeIDNum = each.key 
        let employeeName = self.getName(forUID: employeeIDNum) 

        self.employeeID.append(employeeIDNum) 
        self.name.append(employeeName) 

       } 

       print(self.employeeID) 
       print(self.name) 

      } 

     }) // End observeSingleEvent 

    } 


    func getName(forUID userID: String) -> String{ 

     var empName = "" 

     ref.child("Employee").child(userID).observe(DataEventType.value, with: { (snapshot) in 
      if let value = snapshot.value as? NSDictionary { 

       empName = (value["name"] as? String)! 
      } 
     }) 

     return empName 
    } 

結果：

["0001", "0002", "0003", "0004"] 
["", "", "", ""] 

全碼：

@IBAction FUNC downloadButtonAction（_發件人：UIButton的）{

ref.child("events").child(eventKeyLabel.text!).child("participants").observeSingleEvent(of: .value, with: {(snapshot) in 

    // get the dictionary from the snapshot 
    if let participantsDict = snapshot.value as? [String : AnyObject] { 


     for each in participantsDict { 

      let employeeIDNum = each.key 
      self.getName(forUID: employeeIDNum) { empName in 
       self.name.append(empName) 
       print(empName) 
      } 

      self.employeeID.append(employeeIDNum) 


     } 

     print(self.employeeID) 
     print(self.name) 

    } 

}) // End observeSingleEvent 

}

FUNC的getName（forUID用戶名：字符串，回調：@escaping（字符串） - >無效）{

ref.child("Employee").child(userID).observe(DataEventType.value, with: { (snapshot) in 
    if let value = snapshot.value as? NSDictionary { 
     print(value) 
     if let empName = value["name"] as? String{ 
      callback(empName) 
     } 
    } 
}) 

}

不退還員工姓名。請幫忙。謝謝！

Answer 1

問題是，由於從火力此取是一個異步調用，所以你必須使用回調以獲取名稱到您所呼叫的GetName方法的功能，你可以做這樣的事情：

@IBAction func downloadButtonAction(_ sender: UIButton) { 

     ref.child("events").child(eventKeyLabel.text!).child("participants").observeSingleEvent(of: .value, with: {(snapshot) in 

      // get the dictionary from the snapshot 
      if let participantsDict = snapshot.value as? [String : AnyObject] { 


       for each in participantsDict { 

        let employeeIDNum = each.key 
        self.getName(forUID: employeeIDNum) 

        self.employeeID.append(employeeIDNum) 


       } 

       print(self.employeeID) 
       print(self.name) 

      } 

     }) // End observeSingleEvent 

    } 


    func getName(forUID userID: String) { 



     ref.child("Employee").child(userID).observe(DataEventType.value, with: { (snapshot) in 
      if let value = snapshot.value as? NSDictionary { 
       print(value) //add here 
       if let empName = value["name"] as? String{ 
         self.name.append(empName) 

       } 
      } 
     }) 


    }