通过嵌套的Firebase数据循环填充数组Swift

import Firebase

// 假设Firebase数据库中有一个名为"users"的集合，其中包含多个文档，每个文档都有一个名为"friends"的嵌套字段

struct User {
    var name: String
    var friends: [String]
}

func fetchUsers(completion: @escaping ([User]?) -> Void) {
    let db = Firestore.firestore()
    let usersCollection = db.collection("users")
    
    usersCollection.getDocuments { (snapshot, error) in
        if let error = error {
            print("Error fetching users: \(error.localizedDescription)")
            completion(nil)
            return
        }
        
        var users: [User] = []
        
        for document in snapshot!.documents {
            let data = document.data()
            
            if let name = data["name"] as? String, let friendsData = data["friends"] as? [String] {
                let user = User(name: name, friends: friendsData)
                users.append(user)
            }
        }
        
        completion(users)
    }
}

// 使用示例
fetchUsers { (users) in
    if let users = users {
        for user in users {
            print("User: \(user.name)")
            print("Friends: \(user.friends)")
        }
    }
}