Type Observable<Observable<OrderEntry>> is not assignable to type Observable<number>.
看这行代码:
quantity$: Observable<number> = this.product$.pipe(map(product => this.cartService.getEntry(product.code));
返回的参数类型是:Observable<Observable<OrderEntry>>
![](https://img.haomeiwen.com/i2085791/9389174a5923907a.png)
使用switchMap就可以将嵌套的Observable打平。
![](https://img.haomeiwen.com/i2085791/75af972af70aa832.png)
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