javascript - 对 API 的 Angular 服务调用导致 switchmap 错误
问题描述
我在后端使用带有 Restful C# API 的 Angular。我正在努力创建一个简单的购物车,并且整天都在为此苦苦挣扎。当我在我的页面中调用添加到购物车方法时,逻辑首先检查该项目是否已经在购物车中。如果是,它会增加计数并返回产品,以便状态可以更新。如果产品不在购物车中,则将产品添加到购物车并返回产品对象以更新状态。
最初的呼叫出错了,一切都搞砸了——如果你能帮我弄清楚发生了什么,我将永远感激不尽!
C# 方法
[HttpGet("GetItem/{cartId}/item/{prodId}")]
public async Task<ProductViewModel> GetItem(string cartId, int prodId)
{
var prod = await _shopCartSvc.GetItem(cartId, prodId);
return prod;
}
[HttpGet("CreateItem/{cartId}/item/{prodId}")]
public async Task<ProductViewModel> CreateItem(string cartId, int prodId)
{
var prod = await _shopCartSvc.CreateItem(cartId, prodId);
return prod; // I stop it here to check my return values
}
在角度形式中,我在产品卡组件中有以下逻辑
addToCart() {
console.log('addToCart');
this.cartSvc.addToCart(this.product)
.subscribe((p : Product) => {
this.product = p;
console.log('addToCart.done',p);
});
}
这将调用购物车服务 addToCart 公共方法
addToCart(product: Product) {
console.log('cs.addToCart');
return this.updateItem(product);
}
这又会调用私有 updateItem 方法来完成所有处理
private getItem(cartId: string, productId: number) {
console.log('getItem-productId', productId);
return this.http.get(this.getBaseUrl() + 'GetItem/'+ cartId +'/item/' + productId)
.pipe(
map((response: Product) => {
console.log('getItem-done', response);
return response
}),
catchError(this.handleError));
}
private createItem(cartId: string, productId: number) {
console.log('createItem');
return this.http.get(this.getBaseUrl() + 'CreateItem/'+ cartId + '/item/' + productId)
.pipe(
map((response: Product) => {
console.log('createItem-done', response);
return response
}),
catchError(this.handleError));
}
private updateItem(product: Product, amt: number = 1): Observable<Product> {
let cartId = this.getOrCreateCartId();
return this.getItem(cartId, product.id)
.switchMap(item => {
if (item == null) {
console.log('addItem');
// Create new item in cart
this.createItem(cartId, product.id)
.subscribe(item => {
console.log('addItem.done',item);
return of(item);
});
} else {
let total = item['quantity'] + amt;
if (total > 0) {
// Update qty of existing item in cart
item['quantity'] = total;
console.log('Cart Id',cartId,', UpdateItemQty to', total);
this.http.post(this.getBaseUrl() + 'UpdateItem/'+ cartId, item)
.take(1).switchMap( item => {
console.log('UpdateItem.done - newQty', item['quantity']);
return of(item);
});
} else {
// Qty 0 so remove
console.log('DELETE');
this.http.get(this.getBaseUrl() + 'RemoveItem/'+ cartId + '/item/' + item['id']);
return of (product);
} // end if
} // end if
}); // getItem - switchMap
}
在最初将商品添加到购物车期间发生的情况是它会引发错误,但该商品仍在添加中。按照日志消息,我得到
console.js:35 cs.addToCart
console.js:35 getItem-productId 1
console.js:35 getItem-done null
console.js:35 addItem
console.js:35 createItem
console.js:35 Global - Unhandled Error: TypeError: You provided 'undefined' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable.
....
console.js:35 createItem-done {name: "Beagle", description: "", imageUrl: "Beagle.png", defaultTextColor: "Black", isPremiumProduct: false, …}
console.js:35 addItem.done {name: "Beagle", description: "", imageUrl: "Beagle.png", defaultTextColor: "Black", isPremiumProduct: false, …}
我是 Angular 的新手,我一生都无法弄清楚问题所在。我可以进入我的 C# 后端并在 return 语句上停止它以查看返回的值。它是正确的类型和正确的值。当我在后端时发生错误,当我继续流时,它会完成,但由于错误,我的对象状态不会更新。我得到的完整错误是:
console.js:35 Global - Unhandled Error: TypeError: You provided 'undefined' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable.
at subscribeTo (subscribeTo.js:41)
at subscribeToResult (subscribeToResult.js:11)
at SwitchMapSubscriber.push../node_modules/rxjs/_esm5/internal/operators/switchMap.js.SwitchMapSubscriber._innerSub (switchMap.js:51)
at SwitchMapSubscriber.push../node_modules/rxjs/_esm5/internal/operators/switchMap.js.SwitchMapSubscriber._next (switchMap.js:41)
at SwitchMapSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.next (Subscriber.js:54)
at CatchSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber._next (Subscriber.js:77)
at CatchSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.next (Subscriber.js:54)
at MapSubscriber.push../node_modules/rxjs/_esm5/internal/operators/map.js.MapSubscriber._next (map.js:41)
at MapSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.next (Subscriber.js:54)
at MapSubscriber.push../node_modules/rxjs/_esm5/internal/operators/map.js.MapSubscriber._next (map.js:41)
at MapSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.next (Subscriber.js:54)
at FilterSubscriber.push../node_modules/rxjs/_esm5/internal/operators/filter.js.FilterSubscriber._next (filter.js:38)
at FilterSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.next (Subscriber.js:54)
at MergeMapSubscriber.push../node_modules/rxjs/_esm5/internal/operators/mergeMap.js.MergeMapSubscriber.notifyNext (mergeMap.js:84)
at InnerSubscriber.push../node_modules/rxjs/_esm5/internal/InnerSubscriber.js.InnerSubscriber._next (InnerSubscriber.js:15)
at InnerSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.next (Subscriber.js:54)
at XMLHttpRequest.onLoad (http.js:1534)
at XMLHttpRequest.wrapped (raven.js:376)
at ZoneDelegate.push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:423)
at Object.onInvokeTask (core.js:14051)
at ZoneDelegate.push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:422)
at Zone.push../node_modules/zone.js/dist/zone.js.Zone.runTask (zone.js:195)
at ZoneTask.push../node_modules/zone.js/dist/zone.js.ZoneTask.invokeTask [as invoke] (zone.js:498)
at invokeTask (zone.js:1744)
at XMLHttpRequest.globalZoneAwareCallback (zone.js:1781)
解决方案
这里:
if (item == null) {
console.log('addItem');
// Create new item in cart
this.createItem(cartId, product.id)
.subscribe(item => {
console.log('addItem.done',item);
return of(item);
});
}
该项目已创建,因为您有一个 API 调用和一个订阅,但没有返回语句。订阅中的内容不计算在内。如果你想返回一个流并执行一些副作用,你应该
if (item == null) {
console.log('addItem');
// Create new item in cart
return this.createItem(cartId, product.id)
.pipe(tap(item => {
console.log('addItem.done',item);
}))
}
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