如何从存储在 Firestore (Swift) 中的文档中返回对象

Question

我在 firebase 中有一个用户集合和一个用户结构。我需要编写一个函数，接收用户的 id 并返回相应的用户对象：

struct AppUser: Codable {

    var id: String
    var displayName: String
    var photoURL: String
    var points: Int?
    var knownLanguageCodes: Set<String>?

}

这是我目前拥有的功能。

func getUser(id: String) -> AppUser? {

    let db = Firestore.firestore()
    let userRef = db.collection("users").document(id)

    userRef.getDocument { (document, error) in
         if let document = document, document.exists {
            let userID = document.data()?["id"] as! String
            let userDisplayName = document.data()?["displayName"] as! String
            let userPhotoURL = document.data()?["photoURL"] as! String
            let userPoints = document.data()?["points"] as! Int?
            let userKnownLanguageCodes = document.data()?["knownLanguageCode"] as! Set<String>?
            let user = AppUser(id: userID,
                               displayName: userDisplayName,
                               photoURL: userPhotoURL,
                               points: userPoints,
                               knownLanguageCodes: userKnownLanguageCodes)
            return user
         } else {
            print("Error getting user")
            return nil
        }
    }
}

上面的两个return语句都给出了错误：Unexpected non-void return value in void function

我在https://cloud.google.com/firestore/docs/query-data/get-data 的“自定义对象”标题下查看了代码，它似乎对我不起作用。我收到错误：“NSObject”类型的值没有成员“数据”。这是在链接中代码的第 6 行生成的。

Answer 1

你不能在闭包内返回使用类似的完成

func getUser(id: String,completion:@escaping((AppUser?) -> ())) {

    let db = Firestore.firestore()
    let userRef = db.collection("users").document(id) 
    userRef.getDocument { (document, error) in
         if let document = document, document.exists {
            let userID = document.data()?["id"] as! String
            let userDisplayName = document.data()?["displayName"] as! String
            let userPhotoURL = document.data()?["photoURL"] as! String
            let userPoints = document.data()?["points"] as! Int?
            let userKnownLanguageCodes = document.data()?["knownLanguageCode"] as! Set<String>?
            let user = AppUser(id: userID,
                               displayName: userDisplayName,
                               photoURL: userPhotoURL,
                               points: userPoints,
                               knownLanguageCodes: userKnownLanguageCodes)
            completion(user)
         } else {
            print("Error getting user")
            completion(nil)
        }
    }
}

---

打电话

getUser(id:<#str#>) { user in
  print(user)
}