Angular - handling Observable<T> responses when using Http.post

Question

Angular - handling Observable<T> responses when using Http.post

One issue I encountered was when trying to implement a method that returns an Observable. Within this method, I utilized http.post to send a request to the backend. My goal was to store the JSON object response in an Observable variable and return it. However, I faced difficulty in achieving this. When attempting to assign the 'res' variable from .subscribe to the 'postResponse' variable, I found that 'postResponse' remained empty even though 'res' displayed the correct value in the local console.log. Strangely, the global console.log did not show anything. Additionally, the error message Type 'ArqResponse' is not assignable to type 'Observable' occurred during the return statement.

This is a snippet of my code:

postARQRequest(request): Observable<ArqResponse>{
    let postResponse = new ArqResponse;
    const result = this.http.post<ArqResponse>(this.arqUrl, request)
                       .subscribe((res: ArqResponse) => { postResponse = res; console.log('shadow: ' + res)});
    console.log('global: ' + JSON.stringify(postResponse));
    return postResponse;
}

In light of these challenges, I have the following questions:

How can I successfully store the response body in a variable for later retrieval?
What is the proper way to convert an ArqResponse variable into an Observable variable?
Why am I encountering an error stating that '.subscribe' is not a function?

angular typescript rxjs observable rxjs6

Answer 1

Answer №1

It seems like this might be the solution you're looking for:

postARQRequest(request): Observable<ArqResponse>{
    return this.http.post<ArqResponse>(this.arqUrl, request);
}

You don't need to subscribe to anything in this case. Since this.http.post already returns the desired type, simply return it.

If you wish to store the response in a local variable, there are a few ways you could achieve that:

Option 1: Use a promise to get the result and then convert it to an observable using of:

async postARQRequest(request): Observable<ArqResponse>{
    let postResponse = new ArqResponse;
    postResponse = await this.http.post<ArqResponse>(this.arqUrl, request).toPromise();

    return of(postResponse);
}

Option 2: Utilize the tap operator to react to the response without mutating it:

postARQRequest(request): Observable<ArqResponse>{
    return this.http.post<ArqResponse>(this.arqUrl, request).pipe(
        tap((res) => ...) // perform operations on res here, but it won't change the original response
    );
}

Option 3: Use the map operator to transform the response into something else:

postARQRequest(request): Observable<ArqResponse>{
    return this.http.post<ArqResponse>(this.arqUrl, request).pipe(
        map((res) => ...) // manipulate res here, and this method will map to whatever is returned from it
   );
}

Answer 2

It seems like this might be the solution you're looking for:

postARQRequest(request): Observable<ArqResponse>{
    return this.http.post<ArqResponse>(this.arqUrl, request);
}

You don't need to subscribe to anything in this case. Since this.http.post already returns the desired type, simply return it.

If you wish to store the response in a local variable, there are a few ways you could achieve that:

Option 1: Use a promise to get the result and then convert it to an observable using of:

async postARQRequest(request): Observable<ArqResponse>{
    let postResponse = new ArqResponse;
    postResponse = await this.http.post<ArqResponse>(this.arqUrl, request).toPromise();

    return of(postResponse);
}

Option 2: Utilize the tap operator to react to the response without mutating it:

postARQRequest(request): Observable<ArqResponse>{
    return this.http.post<ArqResponse>(this.arqUrl, request).pipe(
        tap((res) => ...) // perform operations on res here, but it won't change the original response
    );
}

Option 3: Use the map operator to transform the response into something else:

postARQRequest(request): Observable<ArqResponse>{
    return this.http.post<ArqResponse>(this.arqUrl, request).pipe(
        map((res) => ...) // manipulate res here, and this method will map to whatever is returned from it
   );
}

Answer 3

Answer №2

Perhaps this information will be useful to you

sendARQRequest(): Observable<ArqResponse[]> {
 return this.http.post(this.arqUrl, request)
 .map(this.extractData()) <== result from function is passed here
 .catch(this.handleError()); <== result from function is passed here
}

Process the response and handle errors in this section

private extractData(res: Response) {
   let body = res.json(); 
   return body.data || { }; 
}

private handleError (error: any) {
    let errMsg = error.message || 'Server error';
    console.error(errMsg); 
    return Observable.throw(errMsg);
}

Answer 4

Perhaps this information will be useful to you

sendARQRequest(): Observable<ArqResponse[]> {
 return this.http.post(this.arqUrl, request)
 .map(this.extractData()) <== result from function is passed here
 .catch(this.handleError()); <== result from function is passed here
}

Process the response and handle errors in this section

private extractData(res: Response) {
   let body = res.json(); 
   return body.data || { }; 
}

private handleError (error: any) {
    let errMsg = error.message || 'Server error';
    console.error(errMsg); 
    return Observable.throw(errMsg);
}

Answer 5

Answer №3

The function http.post already provides an Observable, allowing you to simplify your code like this:

postARQRequest(request): Observable<ArqResponse>{
    return this.http.post<ArqResponse>(this.arqUrl, request);
}

Then, you can simply subscribe to it:

this.arqService.postARQRequest(...).subscribe()

If you need to convert an object to an Observable, you can make use of of from Rxjs6:

import { of } from 'rxjs';

// ...

// convert a value into an Observable:
of(someObject);

Answer 6

The function http.post already provides an Observable, allowing you to simplify your code like this:

postARQRequest(request): Observable<ArqResponse>{
    return this.http.post<ArqResponse>(this.arqUrl, request);
}

Then, you can simply subscribe to it:

this.arqService.postARQRequest(...).subscribe()

If you need to convert an object to an Observable, you can make use of of from Rxjs6:

import { of } from 'rxjs';

// ...

// convert a value into an Observable:
of(someObject);

Angular - handling Observable<T> responses when using Http.post

Answer №1

Answer №2

Answer №3

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