无法让 Firestore 将快照文档转换为“照片”对象

Question

我在将使用 Firebase 实时数据库的 getPhotos 方法迁移到使用 Firestore 的 getPhotos1 时遇到问题，但由于某种原因无法将 getPhotos1 中的文档快照获取到 Photos1 对象。

这是我使用 Firebase 实时数据库的 getPhotos 方法：

static func getPhotos (completion: @escaping ([Photo]) -> Void) {

    //Getting a reference to the database
    let dbRef = Database.database().reference()

    //Make the db call
    dbRef.child("photos").observeSingleEvent(of: .value) { (snapshot) in

        //Declare an array to hold the photos
        var retrievedPhotos = [Photo]()

        //Get the list of snapshots
        let snapshots = snapshot.children.allObjects as? [DataSnapshot]

        if let snapshots = snapshots {

            //Loop through each snapshot and parse out the photos
            for snap in snapshots {

                //Try to create a photo from a snapshot
                let p = Photo(snapshot: snap)

                //If successful, then add it to our array
                if p != nil {
                    retrievedPhotos.insert(p!, at: 0)

                }
            }
        }
        //After parsing the snapshots, call the completion closure
        completion(retrievedPhotos)
    }
}

这是它的对象

import Foundation
import RealmSwift
import FirebaseDatabase
import Firebase

class Photo: Object {

    @objc dynamic var photoId:String?
    @objc dynamic var byId:String?
    @objc dynamic var byUsername:String?
    @objc dynamic var date:String?
    @objc dynamic var url:String?
    @objc dynamic var postId:String?

    override static func primaryKey() -> String? {
        return "photoId"
    }

    override static func indexedProperties() -> [String] {
        return ["byUsername"]
    }

    convenience init?(snapshot:DataSnapshot){
        self.init ()

        //Photo data
        let photoData = snapshot.value as? [String:String]

        if let photoData = photoData {

            let photoId = snapshot.key
            let byId = photoData["byId"]
            let byUsername = photoData["byUsername"]
            let date = photoData["date"]
            let url = photoData["url"]
            let postId = photoData["postId"]

            guard byId != nil && byUsername != nil && date != nil && url != nil && postId != nil else {
                return nil
            }
            self.photoId = photoId
            self.byId = byId
            self.byUsername = byUsername
            self.date = date
            self.url = url
            self.postId = postId

        }
    }
}

这是我使用 Firestore 的 getPhotos1 方法，不起作用：

    static func getPhotos1 (completion: @escaping ([Photo1]) -> Void) {

    //Get a Firebase reference
    let db = Firestore.firestore()
    db.collection("posts").getDocuments() {snapshot, error  in

        //Declare an array to hold the photos
        var retrievedPhotos = [Photo1]()

        if error == nil && snapshot != nil {
            for document in snapshot!.documents {
                let p = Photo1(snapshot: document)
                print(p!)
                if p != nil {
                retrievedPhotos.insert(p!, at: 0)
                //print("retrievedPhotos: \(retrievedPhotos)")
                }
            }
        }
        //After parsing the snapshots, call the completion closure
        completion(retrievedPhotos)
    }
}

这就是它的对象

class Photo1: Object {

@objc dynamic var photoId:String?
@objc dynamic var byId:String?
@objc dynamic var byUsername:String?
@objc dynamic var date:String?
@objc dynamic var url:String?
@objc dynamic var postId:String?

override static func primaryKey() -> String? {
    return "photoId"
}

override static func indexedProperties() -> [String] {
    return ["byUsername"]
}

convenience init?(snapshot:DocumentSnapshot){
    self.init ()

    //Photo data
    let photoData = snapshot.data() as? [String:String]

    if let photoData = photoData {

        let photoId = snapshot.documentID
        let byId = photoData["byId"]
        let byUsername = photoData["byUsername"]
        let date = photoData["date"]
        let url = photoData["url"]
        let postId = photoData["postId"]

        guard byId != nil && byUsername != nil && date != nil && url != nil && postId != nil else {
            return nil
        }
        self.photoId = photoId
        self.byId = byId
        self.byUsername = byUsername
        self.date = date
        self.url = url
        self.postId = postId

    }
}
}

10 月 1 日编辑： 更新了 getPhoto1 方法。

static func getPhotos1 (completion: @escaping ([Photo1]) -> Void) {

    //Get a Firebase reference
    let db = Firestore.firestore()
    db.collection("posts").getDocuments() { (snapshot, error)  in

        //Declare an array to hold the photos
        var retrievedPhotos = [Photo1]()
        print("This is snapshot: \(String(describing: snapshot))")

        if error == nil && snapshot != nil {

            for document in snapshot!.documents {

                let documentData = document.data()

                print("This is DocData: \(documentData)")

                let p = Photo1(snapshot: documentData)
                print("This is p: \(p)")
                if p != nil {
                retrievedPhotos.insert(p!, at: 0)
                print("retrievedPhotos: \(retrievedPhotos)")
                }}}
        //After parsing the snapshots, call the completion closure
        completion(retrievedPhotos)
    }}

但是我收到了这个错误：

Cannot convert value of type '[String : Any]' to expected argument type 'DocumentSnapshot'

提前感谢您的建议。

我试图搜索以前的帖子，虽然有一些，但我无法弄清楚，因为它们不是 Swift 特定的。

Answer 1

问题中的代码存在许多问题；我认为这三种不同的 API（Firebase 实时数据库、Firestore 和 Realm）可能会造成一些混乱。

让我们用 Firestore 的直接答案切入正题。此代码将读取 Firestore 集合中的文档，根据该数据创建 PhotoClass 对象并将它们存储在数组中。假设结构是这样的

photos //a collection
   photo_0 //a document
      byUserName: "Henry"
      byId: "uid_0"
   photo_1
      byUserName: "George"
      byId: "uid_1"

这是一个 PhotoClass - 我将属性默认为空字符串而不是 nil，以减少处理 nil 的需要。由于我们没有使用 Realm，因此我还删除了 Object 定义并将 vars 更改为 Swift vars 而不是 Realm 所需的 ObjC vars（@objc 动态）

class PhotoClass {
    var photoId = ""
    var byId = ""
    var byUsername = ""
    //var date:String?
    //var url:String?
    //var postId:String?

    init(withDocumentSnapshot: DocumentSnapshot) {
        self.photoId = withDocumentSnapshot.documentID
        self.byUsername = withDocumentSnapshot.get("userName") as? String ?? "No User Name"
        self.byId = withDocumentSnapshot.get("byId") as? String ?? "No uid"
    }
}

请注意，如果读取的属性为零，我会将值默认为已知字符串。这样，如果属性丢失或为零，应用程序就不会崩溃。如果你想使用 nil 值，那很酷，但你必须通过在整个过程中安全地使用它们来保护你的代码。

然后是一个数组来存储照片的

var photosArray = [PhotoClass]()

然后是读取照片节点中所有文档的代码，创建 PhotoClass 对象并填充数组

func readAllPhotos() {
    let photosCollection = self.db.collection("photos")
    photosCollection.getDocuments(completion: { snapshot, err in
        if let err = err {
            print(err.localizedDescription)
            return
        }

        for doc in snapshot!.documents {
            let photo = PhotoClass(withDocumentSnapshot: doc)
            self.photosArray.append(photo)
        }
    })
}

再次注意，有代码可以检查错误并在未找到节点或发生其他错误时保护应用程序。