如何统计Firebase数据库中所有客户的“Open service”状态数量？

你的数据库结构为userDatabase/userID/Customers，包含两位客户，路径示例如下：

usersDatabase g8voYf1yoChnpmhkoPgtmO4FQT62 - (uid)
  Customers
    Tom Smith (customer with custom ID)
      -LDFZw1tca8KOrnqyyWH - (auto id of customer child)
        Status of Service: "Open service"
    Ben Thomas (customer with custom ID)
      -LDFZw1tca8KOjgoenBN - (auto id of customer child)
        Status of Service: "Open service"

你希望统计数据库中状态为Open service的客户总数，但目前仅能逐个打印状态值。现有取值代码如下：

let userID = Auth.auth().currentUser?.uid
let usersDatabaseRef = Database.database().reference().child("usersDatabase").child(userID!).child("Customers")
usersDatabaseRef.observe(.value, with: { snapshot in
    var totalCustomerCount = 0
    for child in snapshot.children {
        let childSnap = child as! DataSnapshot
        let childrenRef = childSnap
        totalCustomerCount += Int(childrenRef.childrenCount)
        print("user \(childSnap.key) has \(childrenRef.childrenCount) customers")
        let userCustomerSnap = childSnap
        for customer in userCustomerSnap.children.allObjects as! [DataSnapshot] {
            let customerSnap = customer
            let dict = customerSnap.value as! [String: Any]
            let stat = dict["Status of Service"] as! String
            let myStatistic = PrintModel(status: stat)
            self.statistic.append(myStatistic)
            print("Statistic: \(String(describing: myStatistic.status))")
        }
    }
    print("... and there are \(totalCustomerCount) total customers")
})

当前日志输出：

1. user Tom Smith has 1 customers
2. Statistic: Optional("Open service")
3. user Ben Thomas has 1 customers
4. Statistic: Optional("Open service")

你期望的输出为：

1. Statistic: 2

很容易实现这个统计需求，我们只需要新增一个专门的计数器，遍历客户时判断状态并累加即可。修改后的代码如下：

let userID = Auth.auth().currentUser?.uid
let usersDatabaseRef = Database.database().reference().child("usersDatabase").child(userID!).child("Customers")
usersDatabaseRef.observe(.value, with: { snapshot in
    // 初始化计数器，专门统计"Open service"的数量
    var openServiceCount = 0
    
    for child in snapshot.children {
        let childSnap = child as! DataSnapshot
        for customer in childSnap.children.allObjects as! [DataSnapshot] {
            let dict = customer.value as! [String: Any]
            // 用可选绑定避免强制解包导致崩溃
            if let stat = dict["Status of Service"] as? String {
                if stat == "Open service" {
                    openServiceCount += 1
                }
                // 若仍需保存所有状态记录，保留这部分代码
                let myStatistic = PrintModel(status: stat)
                self.statistic.append(myStatistic)
            }
        }
    }
    // 打印最终统计结果
    print("Statistic: \(openServiceCount)")
})

关键改动说明： #

• 新增openServiceCount变量，初始值为0，专门用于统计符合条件的状态数量
• 对状态值使用可选绑定if let stat = ...，避免强制解包引发崩溃
• 遍历每个客户时，判断状态是否等于Open service，符合条件则计数器加1
• 移除了不需要的总客户数统计代码（若需要可保留），最后直接输出统计好的结果

运行修改后的代码，就能得到你想要的Statistic: 2输出啦。

内容的提问来源于stack exchange，提问作者Krzysztof Łowiec