如何编写 Angular ngFor 管道以按对象 属性 过滤对象数组?

How can I write an Angular ngFor pipe to filter array of objects by object property?

我有 2 个 select。

一个用于 Leagues 一个用于 Divisions

我想创建一个 Pipe 来过滤 Divisions 取决于 League 是什么 selected。

提供以下数据。如果我 select Random Beer League 只有 TwoFourSixPack 应该显示为 Divisions select.

的选项
leagues = [
  {id: 1, leagueName: 'Recreation League' },
  {id: 2, leagueName: 'Random Beer League' } 
];

divisions = [
  {id: 1, divisionName: 'SoGreen', leagueId: 1, leagueName: 'Recreation League' },
  {id: 2, divisionName: 'Yellow', leagueId: 1, leagueName: 'Recreation League' },
  {id: 3, divisionName: 'TwoFour', leagueId: 2, leagueName: 'Random Beer League' },
  {id: 4, divisionName: 'SixPack', leagueId: 2, leagueName: 'Random Beer League' }
];

PLUNKER to show the setup

*注意 - plunker 中的数据是硬编码的,但在我的应用程序中设置了它的 Observable。

我已经创建了一个自定义管道并用它来过滤分区下拉列表。

@Pipe({
    name: 'myfilter',
    pure: false
})

export class MyFilterPipe implements PipeTransform {
    transform(items: any[], args: any[]): any {
        return items.filter(item => item.leagueName.indexOf(args.leagueName) > -1);
    }
}


<option *ngFor="let division of divisions | myfilter:leagueSelected" [ngValue]="division">{{division.divisionName}}</option>

请看这个Plnkr