如何在 Firebase onSnapshot 中使用 .catch

Question

我创建了一个 Ionic Firebase 聊天应用程序。我认为我遇到的问题是我在消息页面初始化时设置了一个查询快照，如下所示：

  ngOnInit() {
      this.messageService.getAllMessages()
      .doc(`${this.userId[0] + '-' + this.userId[1]}`)
      .collection('message')
      .orderBy('createdAt', 'asc')
      .onSnapshot((doc) => {
        this.messages = [];
        doc.forEach((snap) => {
          this.messages.push({
            content: snap.data().content,
            createdAt: snap.data().createdAt,
            userId: snap.data().userId
          });
        });
        console.log('messages', this.messages);
      });
  }

问题是，如果第一次尝试发送消息时没有消息，我第一次尝试访问该页面时不会加载该页面。

该消息有点模糊，但我很确定我遇到了这个问题，因为 Firebase 没有返回任何数据，但无法在查询中添加 .catch 来捕获错误并处理它，以便用户可以仍然导航到消息页面。

ERROR Error: Uncaught (in promise): Error: No value accessor for form control with unspecified name attribute
Error: No value accessor for form control with unspecified name attribute
    at _throwError (vendor.js:70776)
    at setUpControl (vendor.js:70646)
    at NgModel._setUpStandalone (vendor.js:73693)
    at NgModel._setUpControl (vendor.js:73668)
    at NgModel.ngOnChanges (vendor.js:73604)
    at checkAndUpdateDirectiveInline (vendor.js:63813)
    at checkAndUpdateNodeInline (vendor.js:65493)
    at checkAndUpdateNode (vendor.js:65432)
    at debugCheckAndUpdateNode (vendor.js:66400)
    at debugCheckDirectivesFn (vendor.js:66343)
    at resolvePromise (polyfills.js:3193)
    at resolvePromise (polyfills.js:3150)
    at polyfills.js:3254
    at ZoneDelegate.push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invokeTask (polyfills.js:2785)
    at Object.onInvokeTask (vendor.js:57358)
    at ZoneDelegate.push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invokeTask (polyfills.js:2784)
    at Zone.push../node_modules/zone.js/dist/zone.js.Zone.runTask (polyfills.js:2557)
    at drainMicroTaskQueue (polyfills.js:2963)
defaultErrorLogger @ vendor.js:55398
handleError @ vendor.js:55450
next @ vendor.js:57952
schedulerFn @ vendor.js:52576
__tryOrUnsub @ vendor.js:133918
next @ vendor.js:133857
_next @ vendor.js:133804
next @ vendor.js:133781
next @ vendor.js:133566
emit @ vendor.js:52556
(anonymous) @ vendor.js:57389
push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invoke @ polyfills.js:2753
push../node_modules/zone.js/dist/zone.js.Zone.run @ polyfills.js:2512
runOutsideAngular @ vendor.js:57315
onHandleError @ vendor.js:57389
push../node_modules/zone.js/dist/zone.js.ZoneDelegate.handleError @ polyfills.js:2757
push../node_modules/zone.js/dist/zone.js.Zone.runGuarded @ polyfills.js:2526
_loop_1 @ polyfills.js:3056
api.microtaskDrainDone @ polyfills.js:3065
drainMicroTaskQueue @ polyfills.js:2970
Promise.then (async)
scheduleMicroTask @ polyfills.js:2946
push../node_modules/zone.js/dist/zone.js.ZoneDelegate.scheduleTask @ polyfills.js:2775
onScheduleTask @ polyfills.js:2663
push../node_modules/zone.js/dist/zone.js.ZoneDelegate.scheduleTask @ polyfills.js:2766
push../node_modules/zone.js/dist/zone.js.Zone.scheduleTask @ polyfills.js:2600
push../node_modules/zone.js/dist/zone.js.Zone.scheduleMicroTask @ polyfills.js:2620
scheduleResolveOrReject @ polyfills.js:3241
resolvePromise @ polyfills.js:3187
(anonymous) @ polyfills.js:3103
webpackJsonpCallback @ runtime.js:26
(anonymous) @ pages-messages-messages-module.js:1
vendor.js:116244 POST https://firestore.googleapis.com/google.firestore.v1.Firestore/Write/channe

所以我的问题是，有没有办法在 firebase 中处理 .Snapshot 查询中的空返回值？

我试过这个：

  ngOnInit() {
    try {
      this.messageService.getAllMessages()
      .doc(`${this.users[0] + '-' + this.users[1]}`)
      .collection('message')
      .orderBy('createdAt', 'asc')
      .onSnapshot((doc) => {
        this.messages = [];
        doc.forEach((snap) => {
          this.messages.push({
            content: snap.data().content,
            createdAt: snap.data().createdAt,
            userId: snap.data().userId
          });
        });
        console.log('messages', this.messages);
      });
    } catch (error) {
      console.log('Message page error', error);
    }
  }

Answer 1

虽然Doug 的回答是正确的，但您仍然需要onSnapshot在权限被拒绝时捕获错误

为此，请使用以下语法：

const unsubscribeMe = firestoreInstance
    .collection('example')
    .onSnapshot(
        querySnapshot => {
            if (querySnapshot.empty) {
                return
            }
            const organizations = querySnapshot.docs.map(ref => ({
                id: ref.id,
                ...ref.data(),
            }))
        },
        error => {
            console.log(error)
        }
    )

请参阅此处的javascript 参考，其中包含可能适合您需要的其他方法签名。