Swift / Firestore - 如何获取包含嵌套 map 对象的单个文档并将它们发送到结构？

Question

I'm trying to get my data from a single document into a Struct for a Tableview. For some reason when getting a single document from Firestore. It comes back as a key-value pair. I thought it would be a dictionary. The same as when you fetch all documents from a collection. I have several nested maps(photo) inside of a map(photos). How do I get the nested maps and add the individual items into my Struct?

var items: [Item] = [] 
db.collection("items").document("aAZWjpXwo2V05rMOsQjR")
     .getDocument{ (docSnapshot, err) in
     if let err = err {
         print("Error getting documents: \(err)")
     } else {
        for document in docSnapshot!.data()! {
            print("\(document)")
            if let item = Item(dictionary: document){
                 self.items.append(item)
            }
        }
     }
}

struct Item {

    var photoUrl: String
    var item_id: String

    init(photoUrl: String, item_id: String) {
        self.photoUrl = photoUrl
        self.item_id = item_id
    }

    // I don't know how to use key-value pairs in Swift
    // init?(dictionary: (key: String, value: Any)) {

    init?(dictionary: [String: Any]) {

        for photoInfo in dictionary["photos"] {

            let photoData = photoInfo["photo"] as? [String: Any]
            let photoUrl = photoData!["photoUrl"] as! String
            let item_id = photoData!["item_id"] as! String
        }

        self.init(photoUrl: photoUrl!, item_id: item_id!)
    }
}

Answer 1

I was able to get the embedded map items this way. I used [[String: Any]] to fix my issue. I guess an embedded map is treated as an array inside of an array. I'm still learning Swift. It took me over a week to figure this out. Happy coding everyone...

var items: [Item] = [] 
db.collection("items").document("aAZWjpXwo2V05rMOsQjR")
     .getDocument{ (docSnapshot, err) in
     if let err = err {
         print("Error getting documents: \(err)")
     } else {
        if let document = docSnapshot.data(),
            let doc = document["photos"] as? [[String: Any]] {
            for photoInfo in doc {
                if let item = Item(dictionary: photoInfo){
                    self.items.append(item)
                }
            }
     }
}

struct Item {

    var photoUrl: String
    var item_id: String

    init(photoUrl: String, item_id: String) {
        self.photoUrl = photoUrl
        self.item_id = item_id
    }

    // I don't know how to use key-value pairs in Swift
    // init?(dictionary: (key: String, value: Any)) {

    init?(dictionary: [String: Any]) {

        let photoData = dictionary["photo"] as? [String: Any]
        let photoUrl = photoData!["photoUrl"] as! String
        let item_id = photoData!["item_id"] as! String

        self.init(photoUrl: photoUrl!, item_id: item_id!)
    }
}