将2个可观察对象合并/合并为一个

Question

Im trying to combine 2 Observables. The first observable Holds a ShoppingCart class and the second holds a list of ShoppingItems . I want to map the observable with shopping cart items ( Observable<ShoppingItems ) to the instance variable within the ShoppingCart class called shoppingList$ .

Observable 1: Observable<ShoppingCart>

Here's a snippet of the shopping cart class.

export class ShoppingCart {
private shoppingList$: Observable<ShoppingItems> 
private selectedIndex: number;
... etc
}

Observable 2: Observable<ShoppingItems[]> private observable: Observable

Here is the function I am using.

retrieveShoppingCartComplete(shoppingCartId: string): Observable<ShoppingCart> {

/**Returns the requested shopping cart, with the Ids of the shopping items in an array called shoppingCart.ShoppingItems*/
    let shoppingCart$ = this.retrieveShoppingCart_AsEntity(shoppingCartId); 


/** returns an Observable<ShoppingItems[]> of the requested ShoppingItems as entitys*/
    let shoppingItems$ = shoppingCart$.map(shoppingCart => this.leS.retrieveShoppingItemsComplete(shoppingCart.ShoppingItemsIds))

   return shoppingCart$.combineAll(shoppingItems$);
}

However the method above returns an Observable<[ShoppingCart | ShoppingItems[]]> Observable<[ShoppingCart | ShoppingItems[]]> not an Observable<ShoppingCart> with the Observable<ShoppingItems> array assigned to the shoppingList$ instance variable in the ShoppingCart Class

Answer 1

I think combineAll is not what you need here. I'd use flatMap to chain two service calls like this:

retrieveShoppingCartComplete(shoppingCartId: string): Observable<ShoppingCart> {
    return this.retrieveShoppingCart_AsEntity(shoppingCartId)
        .flatMap(shoppingCart => {
            shoppingCart.shoppingList$ = this.leS.retrieveShoppingItemsComplete(shoppingCart.ShoppingItemsIds)
        })
}