我正在尝试从 firestore 获取数据，然后将数据转换为数组。新数组应该是可观察的

Question

我有一个服务，我在其中编写了一个从 friestore 获取数据的方法。

该方法需要 return 一个可观察对象。然后数据被转换并存储在另一个变量中。我想创建一个更新变量的可观察对象。我该怎么办。

我已经尝试使用 Subjects、ReplaySubjects 和 observables 创建观察者，但我想我遗漏了一些东西。但是我得到了这个错误：

core.js:5847 ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'asObservable' of undefined

和

core.js:5847 ERROR TypeError: Cannot read property 'next' of undefined the following is the code.

import { BehaviorSubject, Observable, of, Subscriber, ReplaySubject, Subject} from 'rxjs';

export class ProductsService {

  public List : Product[] = [];
  public productListObservable :  Subject<Product[]>;

  private products(): Observable<Product[]> {

      //returns an observable of type Product[]

      this.firestoreService.getProductsList().subscribe((doc) =>{

        //Fetch data from firestore and 
        //create the new list with updated id's

        this.List = doc.docs.map(prodItem =>{
          let x = prodItem.data()
          let test = {};
          test['id']=prodItem.id;
          test['name'] = x['ProductName'];
          test['category'] = x['ProductCategory'];
          test['tags']= x['ProductTags'];
          test['specs'] = x['ProductSpecs'];
          test['inclusions'] = x['ProductInclusion'];
          test['shortDetails'] = x['ProductShortDetails'];
          test['description'] = x['ProductDescription'];
          test['pictures'] = x['ProductImages'];

          return test;
        })
        this.productListObservable.next(this.List);
     })

    return this.productListObservable.asObservable();

  }


public getProducts(): Observable<Product[]> {
    //var test = this.products();
    //test.subscribe(x =>{
    //  console.log(x);
    //})
    return this.products();
  }

在Component.html

   ngOnInit() {
    this.productsService.getProducts().subscribe(product => this.products = product);
  }

Answer 1

你得到的错误是因为你从未真正创建过你的主题对象。你只是声明了它。你可以改变

public productListObservable :  Subject<Product[]>;

到

public productListObservable = new Subject<Product[]>();

或者，问题的措辞方式，听起来您甚至根本不需要这个主题。如果你只是将它用于 return 一个 Observable，你可以在你现有的 Observable 上使用 rxjs 的 map。类似于：

private products(): Observable<Product[]> {

  //returns an observable of type Product[]

  return this.firestoreService.getProductsList().pipe(map(doc => {

    //Fetch data from firestore and 
    //create the new list with updated id's

    this.List = doc.docs.map(prodItem =>{
      let x = prodItem.data()
      let test = {};
      test['id']=prodItem.id;
      test['name'] = x['ProductName'];
      test['category'] = x['ProductCategory'];
      test['tags']= x['ProductTags'];
      test['specs'] = x['ProductSpecs'];
      test['inclusions'] = x['ProductInclusion'];
      test['shortDetails'] = x['ProductShortDetails'];
      test['description'] = x['ProductDescription'];
      test['pictures'] = x['ProductImages'];

      return test;
    });
    return this.List;
 });

}

我正在尝试从 firestore 获取数据，然后将数据转换为数组。新数组应该是可观察的

I am trying to fetch data from firestore and then convert the data into an array. the new array should be an observable

web

angular

angular-observable

google-cloud-firestore