swift - Firestore - 如果文档不存在，GetDocument() 会使应用程序崩溃

Question

当我尝试获取一个不存在的 Firestore 文档时，我的应用崩溃了

Firestore 文档说我应该得到一个空文档，而不是终端错误 https://firebase.google.com/docs/firestore/query-data/get-data

Note: If there is no document at the location referenced by docRef, the resulting document will be null.

我复制错误的代码如下。对于这次运行，只需使用两个简单的按钮。第一个按钮 (doReadDeepDocument) 读取文档以确保它确实存在。第二个按钮 (doDeleteDeepDocument) 删除文档。请注意，该文档位于子集合中。

import UIKit
import Firestore

class ViewController: UIViewController {

var listenerFriends: FIRListenerRegistration?



@IBAction func doReadDeepDocument(_ sender: Any) {

     print("\nDo Read")
     let db = Firestore.firestore()
     let docRef = db.collection("basic").document("c9qjeO2uSXhPWejYIQ5H").collection("deep").document("4ZgsZJ1xQ3NfDj6BTv3H")

     docRef.getDocument { (document, error) in
        if error != nil {
            print("Error reading the document \(error.debugDescription)")
            return
        }
        print("Inside read completion")
        if let document = document {
            print("SUCCESS GET Document data: \(document.data())")
        } else {
            print("ERROR Document does not exist")
        }
     }
}


@IBAction func doDeleteDeepDocument(_ sender: Any) {
    print("\nDo Delete")
    let db = Firestore.firestore()
    let docRef = db.collection("basic").document("c9qjeO2uSXhPWejYIQ5H").collection("deep").document("4ZgsZJ1xQ3NfDj6BTv3H")

    docRef.delete() { err in
        print("Inside delete completion")
        if let err = err {
            print("Error removing document: \(err)")
        } else {
            print("Document successfully removed!")
        }
    }

}


@IBAction func doBasicWrite(_ sender: Any) {
    var values = [String : Any]()
    values["fld1"] = 1
    values["fld2"] = "Two"

    let db = Firestore.firestore()
    db.collection("basic").document().setData(values) { (error) in
        if error != nil {
            print("basic write failed \(error.debugDescription)")
        } else {
            print("basic write success")
        }
    }
}

@IBAction func doReadBasicSet(_ sender: Any) {
    let db = Firestore.firestore()
    db.collection("basic").getDocuments() { (querySnapshot, err) in
        if let err = err {
            print("Error getting documents: \(err)")
        } else {
            print("Success getting documents")
            for document in querySnapshot!.documents {
                print("\(document.documentID) => \(document.data())")
            }
        }
    }
}


@IBAction func doDeepWrite(_ sender: Any) {
    var values = [String : Any]()
    values["fldA"] = 1
    values["fldB"] = "BBB"

    let db = Firestore.firestore()
    db.collection("basic").document("c9qjeO2uSXhPWejYIQ5H").collection("deep").document().setData(values) { (error) in
        if error != nil {
            print("deep write failed \(error.debugDescription)")
        } else {
            print("deep write success")
        }
    }
}


@IBAction func doReadDeepSet(_ sender: Any) {

    let db = Firestore.firestore()
    db.collection("basic").document("c9qjeO2uSXhPWejYIQ5H").collection("deep").getDocuments() { (querySnapshot, err) in
        if let err = err {
            print("Error getting documents: \(err)")
        } else {
            print("Success getting documents")
            for document in querySnapshot!.documents {
                print("\(document.documentID) => \(document.data())")
            }
        }
    }

}


@IBAction func doStartListen(_ sender: Any) {

    // Get all my friends
    let db = Firestore.firestore()
    let deepRef = db.collection("basic").document("c9qjeO2uSXhPWejYIQ5H").collection("deep")

    // start listener
    listenerFriends = deepRef.addSnapshotListener { querySnapshot, error in
        guard let snapshot = querySnapshot else {
            print("Error fetching snapshots: \(error!)")
            return
        }
        snapshot.documentChanges.forEach { diff in
            if (diff.type == .added) {
                self.watchFriend_Added( diff : diff )
            }
            if (diff.type == .modified) {
                // could be a case where it is marked as 'modified' but is really 'new'
                // reletive to the start of the listener
                // e.g. it was recently changed but prior to the start of the listen.
                self.watchFriend_Modified( diff : diff )
            }
            if (diff.type == .removed) {
                self.watchFriend_Removed( diff : diff )
            }
        }
    }
}

func watchFriend_Added( diff : DocumentChange) {
    print("\nNew friend: \(diff.document.data())")
    print("ID: \(diff.document.documentID)")
}

func watchFriend_Modified( diff : DocumentChange) {
    print("\nModified friend: \(diff.document.data())")
    print("ID: \(diff.document.documentID)")
}

func watchFriend_Removed( diff : DocumentChange) {
    print("\nRemoved friend: \(diff.document.data())")
    print("ID: \(diff.document.documentID)")
}


@IBAction func doStopListen(_ sender: Any) {

    // Stop listening for changes
    if listenerFriends != nil {
        listenerFriends?.remove()
    }
}

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}


}

-

下面是调试控制台的结果。您可以看到成功读取(按下读取按钮)。这确认数据最初存在并且路径正确。然后您会看到成功删除(按下删除按钮)。然后我再次推送读取，应用程序崩溃了。

Do Read
Inside read completion
SUCCESS GET Document data: ["fldB": EEE, "fldA": 1]

Do Delete
Inside delete completion
Document successfully removed!

Do Read
Inside read completion
2018-03-03 12:09:44.471079-0800 testfs[32914:2379972] *** Terminating app due to uncaught exception 'NonExistentDocumentException', reason: 'Document '<FSTDocumentKey: basic/c9qjeO2uSXhPWejYIQ5H/deep/4ZgsZJ1xQ3NfDj6BTv3H>' doesn't exist. Check document.exists to make sure the document exists before calling document.data.'
*** First throw call stack:
(
    0   CoreFoundation                      0x000000010dce112b __exceptionPreprocess + 171
    1   libobjc.A.dylib                     0x000000010ce28f41 objc_exception_throw + 48
    2   testfs                              0x000000010aaacf0b -[FIRDocumentSnapshot objectForKeyedSubscript:] + 0
    3   testfs                              0x000000010a9ddce4 _T06testfs14ViewControllerC18doReadDeepDocumentyypFySo0G8SnapshotCSg_s5Error_pSgtcfU_ + 1188
    4   testfs                              0x000000010a9ddfbc _T0So16DocumentSnapshotCSgs5Error_pSgIxxx_ACSo7NSErrorCSgIyByy_TR + 124
    5   testfs                              0x000000010aaac2bb __50-[FIRDocumentReference getDocumentWithCompletion:]_block_invoke + 357
    6   testfs                              0x000000010aaac878 __72-[FIRDocumentReference addSnapshotListenerInternalWithOptions:listener:]_block_invoke + 305
    7   libdispatch.dylib                   0x0000000110f352f7 _dispatch_call_block_and_release + 12
    8   libdispatch.dylib                   0x0000000110f3633d _dispatch_client_callout + 8
    9   libdispatch.dylib                   0x0000000110f415f9 _dispatch_main_queue_callback_4CF + 628
    10  CoreFoundation                      0x000000010dca3e39 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
    11  CoreFoundation                      0x000000010dc68462 __CFRunLoopRun + 2402
    12  CoreFoundation                      0x000000010dc67889 CFRunLoopRunSpecific + 409
    13  GraphicsServices                    0x000000011423e9c6 GSEventRunModal + 62
    14  UIKit                               0x000000010e15f5d6 UIApplicationMain + 159
    15  testfs                              0x000000010a9e54f7 main + 55
    16  libdyld.dylib                       0x0000000110fb2d81 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

我是否需要捕获 GetDocument() 在任何地方使用的 fatal error ，或者这是一个将被修复的错误。或者，其他一些建议？

Answer 1

不是在 Xcode 中，但以下应该可以工作:

    if let document = document, document.exists {
        print("SUCCESS GET Document data: \(document.data())")
    } else {