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初始化消息页面时使用以下命令设置了查询快照：

  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，如果初次尝试发送消息时没有消息，则我第一次尝试访问该页面时，页面不会加载。

该消息有点模糊，但是我很确定我遇到了这个问题，因为Firebase不会返回任何数据，但是无法在查询中添加.catch来捕获错误并进行处理，因此用户仍然可以导航到消息页面。

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，是否有办法在Firebase的.Snapshot查询中处理空返回值？

我已经尝试过了：

  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 answer是正确的，但是权限被拒绝

时，您仍然需要捕获onSnapshot的错误。

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)
        }
    )

请参见javascript reference here，其中包含可能满足您需要的其他方法签名。

Answer 2

如果没有找到匹配的文档，Firestore查询不会失败。它只是提供了一个不包含文档的QuerySnapshot。

代码中的doc变量是QuerySnapshot类型的对象（因此，它不是“文档”）。它具有一种称为empty()的方法，可用于查看它是否不包含文档。另外，您可以检查其docs属性的长度是否为零。

.onSnapshot(querySnapshot => {
  if (!querySnapshot.empty()) {
    this.messages = [];
    querySnapshot.forEach((snap) => {
      this.messages.push({
        content: snap.data().content,
        createdAt: snap.data().createdAt,
        userId: snap.data().userId
      });
    });
  }
  else {
    // what do you want to do if there are no documents?
  }
});

根据建议，我使用以下更新了我的代码，并遇到了相同的问题：

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

      console.log('messages', this.messages);
    });
}

<ion-list lines="none" *ngIf="messages.length > 0">
  <ion-item *ngFor="let msg of messages; index as i; trackBy: trackByCreated">
    <div size="9" *ngIf="theirItinerary.userId === msg.userId" class="message other-user">
      <span>{{msg.content}}</span>
      <div class="time" text-right><br> {{msg.createdAt | date: 'short'}}</div>
    </div>
    <div offset="3" size="9" *ngIf="theirItinerary.userId !== msg.userId" class="message me" slot="end">
      <span>{{msg.content}}</span>
      <div class="time" text-right><br> {{msg.createdAt | date: 'short'}}</div>
    </div>
  </ion-item>
</ion-list>
</ion-content>

<ion-footer>
  <ion-toolbar light="light">
    <ion-row align-items-center no-padding>
      <ion-col size="8">
        <textarea autosize maxRows="3" [(ngModel)]="newMsg" class="message-input"></textarea>
      </ion-col>
      <ion-col size="3">
        <ion-button expand="block" fill="clear" color="primary" [disabled]="newMsg === ''" class="msg-btn" (click)="sendMessage()">
          <ion-icon name="ios-send" slot="icon-only"></ion-icon>
        </ion-button>
      </ion-col>
    </ion-row>
  </ion-toolbar>
</ion-footer>

如何在Firebase onSnapshot中使用.catch

2 个答案: