How to Decode JSON Data in Angular 2/4 with the Help of HttpClientModule

Question

How to Decode JSON Data in Angular 2/4 with the Help of HttpClientModule

I am receiving this JSON structure from my asp.net core API:

{
  "contentType": null,
  "serializerSettings": null,
  "statusCode": null,
  "value": {
     "productName": "Test",
     "shortDescription": "Test 123",
     "imageUri": "https://bla.com/bla",
     "productCode": null,
     "continuationToken": null
  }
}

Below is the typescript function I am using to call the API and retrieve the above response:

public externalProduct: ProductVM;


getProductExternal(code: string): Observable<ProductVM> {
    return this.http.get("api/product?productCode=" + code)
        .map((data: ProductVM) => {
            this.externalProduct = data; //not working...
            console.log("DATA: " + data);
            console.log("DATA: " + data['value']);
            return data;
        });    
}

This is how the ProductVM interface looks like:

export interface ProductVM {

    productName: string;
    shortDescription: string;
    imageUri: string;
    productCode: string;
    continuationToken: string;
}

The issue I am facing is that I am unable to deserialize it to a ProductVM object. The console logs only display [object Object]

How can I properly map the contents of the value in my JSON response to a ProductVM object?

Is it correct to assume that data is a ProductVM in the map function? Despite trying various approaches, I have not been able to achieve the desired outcome!

I am uncertain whether I should instruct angular to automatically map the value array in the JSON response to a ProductVM object or if I should modify the ProductVM class by providing a constructor (it's currently an interface) and manually extract the specific values from the JSON?

json angular rest typescript

Answer 1

Answer №1

When using the map method in conjunction with http, the data object is identified as an Object. However, this particular type does not contain the necessary value member for access, resulting in a displeased type checker.

In cases where objects are typed (excluding any), they can only be assigned to untyped objects or those of identical types. The issue arises from trying to assign a Object type data to a different type such as ProductVM.

To circumvent type checking, one solution involves casting the data object as an any untyped object. This allows unrestricted access to methods and members akin to regular Javascript.

getProductExternal(code: string): Observable<ProductVM> {
  return this.http.get("api/product?productCode=" + code)
    .map((data: any) => this.externalProduct = data.value);    
}

Alternatively, consider altering your API so that data can be accessed via data.json(), eliminating the need to bypass type checking since the json() method returns an untyped value.

Keep in mind that utilizing an any object may lack the defined methods of ProductVM when introduced later on. To obtain access to these methods, manually instantiate an instance using new ProductVM() along with Object.assign.

Answer 2

When using the map method in conjunction with http, the data object is identified as an Object. However, this particular type does not contain the necessary value member for access, resulting in a displeased type checker.

In cases where objects are typed (excluding any), they can only be assigned to untyped objects or those of identical types. The issue arises from trying to assign a Object type data to a different type such as ProductVM.

To circumvent type checking, one solution involves casting the data object as an any untyped object. This allows unrestricted access to methods and members akin to regular Javascript.

getProductExternal(code: string): Observable<ProductVM> {
  return this.http.get("api/product?productCode=" + code)
    .map((data: any) => this.externalProduct = data.value);    
}

Alternatively, consider altering your API so that data can be accessed via data.json(), eliminating the need to bypass type checking since the json() method returns an untyped value.

Keep in mind that utilizing an any object may lack the defined methods of ProductVM when introduced later on. To obtain access to these methods, manually instantiate an instance using new ProductVM() along with Object.assign.

Answer 3

Answer №2

Check out the angular documentation: Ensuring Type Safety in HTTP Responses

It is essential to specify the type of data being returned when using the new httpClient (introduced since Angular 4.3). Example: this.http.get<ProductVM>(...

public externalProduct: ProductVM;    
getProductExternal(code: string): Observable<ProductVM> {
        return this.http.get<ProductVM>("api/product?productCode=" + code)
            .map((data: ProductVM) => {
                this.externalProduct = data;
                return data;
            });    
    }

This way, Typescript will ensure a peace of mind for you.

Answer 4

Check out the angular documentation: Ensuring Type Safety in HTTP Responses

It is essential to specify the type of data being returned when using the new httpClient (introduced since Angular 4.3). Example: this.http.get<ProductVM>(...

public externalProduct: ProductVM;    
getProductExternal(code: string): Observable<ProductVM> {
        return this.http.get<ProductVM>("api/product?productCode=" + code)
            .map((data: ProductVM) => {
                this.externalProduct = data;
                return data;
            });    
    }

This way, Typescript will ensure a peace of mind for you.

Answer 5

Answer №3

Have you attempted changing

this.externalProduct = data;

to

this.externalProduct = data.json();

Hopefully this suggestion proves useful!

Answer 6

Have you attempted changing

this.externalProduct = data;

to

this.externalProduct = data.json();

Hopefully this suggestion proves useful!

Answer 7

Answer №4

fetchProductInformation(code: string): Observable<ProductVM> {
    return this.http.get("api/product?productCode=" + code)
        .map(response => {
            this.productData = <ProductVM>response;
            console.log("RESPONSE: " + this.productData);
            return response;
        });    
}

To start off, we need to transform the received data into a JSON format. I assign it to response for clarity. Next, we have to access the value property, as in your dataset, value holds the object corresponding to ProductVM.

I prefer doing it like this:

Service

fetchProductInformation(code: string): Observable<ProductVM> {
        return this.http.get(`api/product?productCode=${code}`)
            .map(response => <ProductVM>response)
            .catch((error: any) => Observable.throw(error.json().error || 'Server error'));    
    }

Component

this.subscription = this.myService.fetchProductInformation(code).subscribe(
  product => this.productData = product,
  error => console.warn(error)
);

Answer 8

fetchProductInformation(code: string): Observable<ProductVM> {
    return this.http.get("api/product?productCode=" + code)
        .map(response => {
            this.productData = <ProductVM>response;
            console.log("RESPONSE: " + this.productData);
            return response;
        });    
}

To start off, we need to transform the received data into a JSON format. I assign it to response for clarity. Next, we have to access the value property, as in your dataset, value holds the object corresponding to ProductVM.

I prefer doing it like this:

Service

fetchProductInformation(code: string): Observable<ProductVM> {
        return this.http.get(`api/product?productCode=${code}`)
            .map(response => <ProductVM>response)
            .catch((error: any) => Observable.throw(error.json().error || 'Server error'));    
    }

Component

this.subscription = this.myService.fetchProductInformation(code).subscribe(
  product => this.productData = product,
  error => console.warn(error)
);

Answer 9

Answer №5

Implemented this strategy with a client that utilizes the following method:

HttpClient.get<GENERIC>(...).

The system is now functioning properly. However, it's puzzling why I don't get a type of T returned from the http client unless I apply the solution detailed in the previous answer.

Below is the code snippet for the client:

// get
get<T>(url: string, params?: [{key: string, value: string}]): Observable<T> {
var requestParams = new HttpParams()

if (params !== undefined) {
  for (var kvp of params) {
    params.push(kvp);
  }
}

return this.httpClient.get<T>(url, {
  observe: 'body',
  headers: this.authHeaders,
  params: requestParams
}).pipe(
  map(
    res => <T>res
  )
);
}

Answer 10

Implemented this strategy with a client that utilizes the following method:

HttpClient.get<GENERIC>(...).

The system is now functioning properly. However, it's puzzling why I don't get a type of T returned from the http client unless I apply the solution detailed in the previous answer.

Below is the code snippet for the client:

// get
get<T>(url: string, params?: [{key: string, value: string}]): Observable<T> {
var requestParams = new HttpParams()

if (params !== undefined) {
  for (var kvp of params) {
    params.push(kvp);
  }
}

return this.httpClient.get<T>(url, {
  observe: 'body',
  headers: this.authHeaders,
  params: requestParams
}).pipe(
  map(
    res => <T>res
  )
);
}

How to Decode JSON Data in Angular 2/4 with the Help of HttpClientModule

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

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