在angular2的服务层上修改对象：无法将订阅分配给可观察的类型

Question

I am new to Angular2 framework so excuse if this is a basic question.

I am handling an object at service layer returned via a http wrapper. This object should be passed to the component, but first the data should be manipulated and only necessary data extracted and forwarded.

When I attempt to do this i receive an error "Subscription is not assignable to the type observable". Here is the code

return this.httpGet<UserInfo[]>(url, {headers}).switchMap(data => data)
.subscribe(
    data => {
        console.log("new values are going to be" + JSON.stringify( data[0].address.addressLine1));
        this.userInfo[0].name = "test name";
        this.UserInfo[0].address.city = data[0].address.city;
        this.UserInfo[0].address.state = data[0].address.state;
    },
);

Now, what makes sense in my mind is to first convert the data inside the subscription as it is streamed back, and then return the object explicitly but this also fails to give the desired output, even if the type is an observable. Coming from a java oop background I cannot see what is the issue here an am thoroughly confused. Any insight is appreciated.

edit : for completion here is where the service call is made -

   this.inputFormControl.valueChanges
.debounceTime(4000)
.switchMap(query => this.userService.search(query))
.subscribe(
    data => {
        this.data = data;
    },
);

Answer 1

In your current code, you have already subscribed to the observable. So that returns a Subscription instead of an observable . Then in your calling function, you are trying to assign this to a observable. Try following pattern

   someFunction() {
    return this.httpGet<UserInfo[]>(url, {headers}).switchMap(data => data)
    }

    callingFuction(){
    someFunction().subscribe(
        data => {
            console.log("new values are going to be" + JSON.stringify( data[0].address.addressLine1));
            this.userInfo[0].name = "test name";
            this.UserInfo[0].address.city = data[0].address.city;
            this.UserInfo[0].address.state = data[0].address.state;
        },
    );
    }

Answer 2

As mentioned in other answer, you are returning a subscription instead of an Observable. Also I don't see why the use of switchMap would be necessary in your service (I assume you have your http request in a service), as you are using it in your component. So I would do map in service, modify the data there and return it to your component.

To point out one more thing, that in your current code you are not returning anything from the http-request, so you need to add a return statement.

return this.httpGet<UserInfo[]>(url, {headers})
  .map(data => {         
     this.UserInfo[0].name = "test name";
     this.UserInfo[0].address.city = data[0].address.city;
     this.UserInfo[0].address.state = data[0].address.state;
     return this.UserInfo; // add return!
  });

Your component code would stay as it is.