Obtaining a Comprehensive Response (not limited to just the body) through Angular 4 HTTP Requests

Question

Obtaining a Comprehensive Response (not limited to just the body) through Angular 4 HTTP Requests

I am currently working on getting a full response from my HTTP calls. Following the guidelines in the Angular documentation, I have set my HTTP call options as {observe: 'response'}

However, when I implement this, I encounter the following error:

The type 'Observable<HttpResponse<IItem[]>>' is not compatible with the type 'Observable<IItem[]>'. The property 'includes' is missing in the 'HttpResponse<IItem[]>' type.

It seems my understanding of Observables and Typing/Casting is not completely clear.

In my HTTP Get request, I am receiving an observable which I am trying to strongly type into an array of items (as shown below)

getItems(): Observable <IItem[]>{
    return this._http.get<IItem[]>(url, {observe: 'response'})
    .do(data => console.log('All: ' + JSON.stringify(data)))
};

I attempted setting

getUsers(): Observable <HttpResponse<IUser[]>>

, which resolved the initial error. However, I encountered another error within my subscribe function when trying to assign the returned data to a local variable this.item = data;, where item is declared as Item[]

The type 'Observable<HttpResponse<IItem[]>>' is not assignable to type 'IItem[]

Therefore, my questions are as follows:

How can I resolve the above error and what are the reasons behind it?
Is it necessary to set the return type for the
```
getItems(): Observable <IItem[]>
```
method if ._http.get<IItem[]> already specifies the expected type of response?

It appears that there may be some fundamental concept that I am misunderstanding leading to this confusion. Any assistance would be greatly appreciated. As I am new to Angular 4, please provide guidance with patience.

javascript angular typescript

Answer 1

Answer №1

When using the <code>HttpClient.get

method, it is important to note that it is defined to utilize a generic type T:

get<T>(url: string, options?: {
    ...
}): Observable<T>;

For example, if you pass <IItem[]> to the get method like this - this._http.get<IItem[]>, based on the definition provided, the get method will return a HttpResponse<IItem[]> object. However, if your method getItems is declared to return IItem[], an error will occur:

The error message states that 'Type 'Observable<HttpResponse<IItem[]>>' is not assignable to type 'Observable<IItem[]>'.

In order to resolve this issue, you need to ensure that you are returning IItem[]. This can be achieved by extracting the body of type IItem[] from HttpResponse<IItem[]> and then returning it. Since the do operator does not return anything, you must use the map operator for this purpose:

this._http.get<IItem[]>('url', { observe: 'response' })
            .do(data => console.log('All: ' + JSON.stringify(data)))
            .map(data => data.body)

Answer 2

When using the <code>HttpClient.get

method, it is important to note that it is defined to utilize a generic type T:

get<T>(url: string, options?: {
    ...
}): Observable<T>;

For example, if you pass <IItem[]> to the get method like this - this._http.get<IItem[]>, based on the definition provided, the get method will return a HttpResponse<IItem[]> object. However, if your method getItems is declared to return IItem[], an error will occur:

The error message states that 'Type 'Observable<HttpResponse<IItem[]>>' is not assignable to type 'Observable<IItem[]>'.

In order to resolve this issue, you need to ensure that you are returning IItem[]. This can be achieved by extracting the body of type IItem[] from HttpResponse<IItem[]> and then returning it. Since the do operator does not return anything, you must use the map operator for this purpose:

this._http.get<IItem[]>('url', { observe: 'response' })
            .do(data => console.log('All: ' + JSON.stringify(data)))
            .map(data => data.body)

Answer 3

Answer №2

Here is a solution that should function properly:

  retrieveItems(): Observable<IItem[]>{
            return this.http
            .fetch<IItem[]>(url, {observe: 'response'})
            .do(response => console.log('All Items: ' + JSON.stringify(response)))
            .map( (res: HttpResponse<IItem[]> )  => res.body )
        };

Answer 4

Here is a solution that should function properly:

  retrieveItems(): Observable<IItem[]>{
            return this.http
            .fetch<IItem[]>(url, {observe: 'response'})
            .do(response => console.log('All Items: ' + JSON.stringify(response)))
            .map( (res: HttpResponse<IItem[]> )  => res.body )
        };

Obtaining a Comprehensive Response (not limited to just the body) through Angular 4 HTTP Requests

Answer №1

Answer №2

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