Question

我有一个带有firebase应用程序的Angular 6 我有一个具有可观察性的服务（我稍后希望多个订阅者收听此可观察性）以及订阅此可观察对象的组件我试图实现的目的是获取auth对象，从中获取userId（UID），然后在数据库中搜索具有该ID的所有文档

该组件在ngOnInit钩子处调用observable，但是在该阶段它仍然为null，所以我得到

无法读取未定义的属性“ subscribe”

问题是，如果我运行代码以填充订阅块内部的可观察对象（以获取auth数据），则无法看到该数据，如果它不在其内部（使用静态UID运行同步）确实正确填充并显示数据这是该服务的代码

import { Injectable, EventEmitter } from '@angular/core';
import { AngularFirestore, AngularFirestoreCollection, DocumentChangeAction } from '@angular/fire/firestore';
import { Expense } from '../model/Expense';
import { Observable, ReplaySubject, Subject, from } from 'rxjs';
import { map } from 'rxjs/operators';
import { AuthService } from '../core/services/auth.service';

@Injectable({
    providedIn: 'root',
})
export class ExpenseService {

    private dbPath = '/expenses';

    expenseDetailEvent: EventEmitter<Expense> = new EventEmitter<Expense>();

    expensesRef: AngularFirestoreCollection<Expense> = null;
    expenses$: Observable<Expense[]>;

    constructor(private db: AngularFirestore, auth: AuthService) {
        auth.user$.subscribe(
            user => {
                this.expensesRef = this.db.collection<Expense>(this.dbPath, ref =>
                    ref.where('clientId', '==', user.uid)
                );
                this.expenses$ = this.expensesRef.snapshotChanges().pipe(
                    map(actions =>
                        actions.map(a => {
                            const data = a.payload.doc.data() as Expense;
                            const id = a.payload.doc.id;
                            return { id, ...data };
                        })
                    )
                );
            },
            error => console.log(error)
        );
    }

    createExpense(expense: Expense): Observable<any> {
        return from(this.expensesRef.add(expense));
    }

    updateExpense(expense: Expense): Observable<any> {
        return from(this.expensesRef.doc(expense.id).update(expense));
    }
}

该组件确实起作用

ngOnInit() {
        this.expenseService.expenses$.subscribe(expenses => this.expenses = expenses);
    }

我注意到所有示例都在组件上调用，但是我觉得数据库调用应该以与普通http api调用类似的方式在服务中提供

更新如果我这样初始化服务

expenses$: Observable<Expense[]> = of([]);

因此，应用程序当然不会崩溃，但我看不到任何数据如果我只是将代码拉到外面，然后使用静态UID呢……（当然user.uid与我粘贴的静态字符串相同）

这是更新的代码

constructor(private db: AngularFirestore, auth: AuthService) {
    console.log('being here ,i see the data on screen using the static uid');
    this.expensesRef = this.db.collection<Expense>(this.dbPath, ref =>
        ref.where('clientId', '==', 'noYVScDtKfNB5aFqRkAJR7ghxio2')
    );
    this.expenses$ = this.expensesRef.snapshotChanges().pipe(
        map(actions =>
            actions.map(a => {
                const data = a.payload.doc.data() as Expense;
                const id = a.payload.doc.id;
                return { id, ...data };
            })
        )
    );
    auth.user$.subscribe(
        user => {
            console.log('if inside here than it will not show any data on screen');

        },
        error => console.log(error)
    );
}

Answer 1

问题在于expenses$仅在auth.user$发出某些东西之后才定义，因为那是在它被分配时。

解决方案1  您可以尝试将ExpenseService服务注入到更高级别组件（甚至是AppComponent）的构造函数中，以便调用ExpenseService的构造函数并分配expenses$ Observable （您只需要注入它，而无需任何方法调用或属性访问）。此时，当您加载组件时，应定义Observable

解决方案2 使用expenses$手动创建Observable of，然后订阅this.expensesRef.snapshotChanges()，您可以在expenses$

中发出值

类似的东西：

...

expensesSubject = new Subject<Expense[]>();
expenses$: from(expensesSubject);

constructor(private db: AngularFirestore, auth: AuthService) {
    auth.user$.subscribe(
        user => {
            this.expensesRef = this.db.collection<Expense>(this.dbPath, ref =>
                ref.where('clientId', '==', user.uid)
            );
            this.expensesRef.snapshotChanges().pipe(
                map(actions =>
                    actions.map(a => {
                        const data = a.payload.doc.data() as Expense;
                        const id = a.payload.doc.id;
                        return { id, ...data };
                    })
                )
            ).subscribe((whatever) => {
              expensesSubject.next(whatever);
            })
        }
    )
}

带有userId的Angular Firestore应用程序查询不起作用

1 个答案: