如何过滤来自 Firestore 数据库的数据

Question

我想在我的代码上实现这个过滤，但我在实现它时遇到了问题。我在实现这行代码时出错：function search(text: string, pipe: PipeTransform): Country[] {  return COUNTRIES.filter(country => {    const term = text.toLowerCase();    return country.name.toLowerCase().includes(term)        || pipe.transform(country.area).includes(term)        || pipe.transform(country.population).includes(term);  });}我无法更改COUNTRIES.filter，当我尝试在其上放置/替换我的函数时出现错误。我收到此错误“ 'void'类型上不存在属性'过滤器' ”这是我的代码。export class MyComponent implements OnInit {  countries: Observable<any[]>;  filter = new FormControl('');  listQuestions = [];  constructor(private extractorService: ExtractorService,               private fstore: AngularFirestore) { }  ngOnInit() {   this.filterFunction();  }  filterFunction(){    this.countries = this.filter.valueChanges.pipe(      startWith(''),      map(text => this.search(text))    );  }  search(text: string): any[] {    return this.sampleFunction().filter(country => {      const term = text.toLowerCase();        return country.caseID.toLowerCase().includes(term)            || (country.word).toLowerCase().includes(term)            || (country.product).toLowerCase().includes(term);    });  }  sampleFunction() {    this.extractorService.dbFirestore().subscribe(data => {      this.listQuestions = data.map(x => {        return x.payload.doc.data();      })    })  }我可以从我的sampleFunction()获取来自 firebase 的所有数据。顺便说一句，我使用以下代码在 html 上加载数据：<tr *ngFor="let item of countries | async">您能帮我将我在sampleFunction()上获得的数据用于指南使用“ return COUNTRIES.filter(country => {”行的搜索功能吗

Answer 1

您不会将 observable 全部返回到async管道中。您正在执行手动订阅并映射结果。

filterFunction() {

  this.countries = this.filter.valueChanges.pipe(

    startWith(''),

    switchMap(text => this.search(text))

  );

}

search(text: string): Observable<any[]> {

  return this.sampleFunction().pipe(

    map(countries => {

      return countries.filter(country => {

        const term = text.toLowerCase();

        return country.caseID.toLowerCase().includes(term)

          || (country.word).toLowerCase().includes(term)

          || (country.product).toLowerCase().includes(term);

      });

    });

  );

}

sampleFunction(): Observable<any[]> {

  return this.extractorService.dbFirestore().pipe(

    map(data => data.map(x => x.payload.doc.data()))

  );

}

我建议尽可能向函数添加返回类型，Typescript 非常擅长发现像这样的基于类型的小错误。

现在的一个潜在问题是this.extractorService.dbFirestore()每次过滤器值更改时都会调用它。如果你不希望这种情况发生，你需要一种不同的方法。

处理静态数据

您可能只想先加载数据，然后过滤固定数组。在这种情况下，您将首先加载数据，然后将值更改与concatMap.

filteredCountries$: Observable<any[]>;

private countries: any[];

filterFunction() {

  // load the countries first

  this.filteredCountries$ = this.getCountries().pipe(

    // set the countries

    tap(countries => this.countries = countries),

    // now start observing the filter changes

    concatMap(countries => {

      return this.filter.valueChanges.pipe(

        startWith(''),

        map(text => this.search(text))

    })

  );

}

search(text: string): any[] {

  return countries.filter(country => {

    const term = text.toLowerCase();

    return country.caseID.toLowerCase().includes(term)

      || (country.word).toLowerCase().includes(term)

      || (country.product).toLowerCase().includes(term);

  });

}

getCountries(): Observable<any[]> {

  return this.extractorService.dbFirestore().pipe(

    map(data => data.map(x => x.payload.doc.data()))

  );

}

然后您的 HTML 将被观看filteredCountries$而不是countries.

<tr *ngFor="let item of filteredCountries$ | async">