So I'm getting the following 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
}
}
I have the following typescript function that invokes the API to get 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;
});
}
ProductVM:
export interface ProductVM {
productName: string;
shortDescription: string;
imageUri: string;
productCode: string;
continuationToken: string;
}
My problem is that I can't deserialize it to ProductVM. The console logs just produce [object Object]
How can I actually map the contents of the value in my json response to a ProductVM object?
Is it wrong to say that data is a ProductVM in the map function? I have tried lots of different combinations but I cannot get it to work!
I'm unsure whether I can somehow automatically tell angular to map the value array in the json response to a ProductVM object or if I should provide a constructor to the ProductVM class (it's an interface right now), and extract the specific values in the json manually?
The data object in the map method chained to http is considered a Object typed object. This type does not have the value member that you need to access and therefore, the type checker is not happy with it.
Objects that are typed (that are not any) can only be assigned to untyped objects or objects of the exact same type. Here, your data is of type Object and cannot be assigned to another object of type ProductVM.
One solution to bypass type checking is to cast your data object to a any untyped object. This will allow access to any method or member just like plain old Javascript.
getProductExternal(code: string): Observable<ProductVM> {
return this.http.get("api/product?productCode=" + code)
.map((data: any) => this.externalProduct = data.value);
}
Another solution is to change your API so that data can deliver its content with data.json(). That way, you won't have to bypass type checking since the json() method returns an untyped value.
Be carefull though as your any object wil not have methods of the ProductVM if you ever add them in the future. You will need to manually create an instance with new ProductVM() and Object.assign on it to gain access to the methods.
From angular documentation: Typechecking http response
You have to set the type of returned data when using new httpClient ( since angular 4.3 ) => 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; // should be allowed by typescript now
return data;
});
}
thus typescript should leave you in peace
Have you tried to replace
this.externalProduct = data;
with
this.externalProduct = data.json();
Hope it helps
getProductExternal(code: string): Observable<ProductVM> {
return this.http.get("api/product?productCode=" + code)
.map(data => {
this.externalProduct = <ProductVM>data;
console.log("DATA: " + this.externalProduct);
return data;
});
}
So, first we convert the response into a JSON.
I store it into response just to make it cleaner. Then, we have to navigate to value, because in your data value is the object that corresponds to ProductVM.
I would do it like this though:
Service
getProductExternal(code: string): Observable<ProductVM> {
return this.http.get(`api/product?productCode=${code}`)
.map(data => <ProductVM>data)
.catch((error: any) => Observable.throw(error.json().error || 'Server error'));
}
Component
this.subscription = this.myService.getProductExternal(code).subscribe(
product => this.externalProduct = product,
error => console.warn(error)
);
I used this approach in a client which uses the method
HttpClient.get<GENERIC>(...).
Now it is working. Anyway, I do not understand, why I do not receive a type of T back from the http client, if I don't use the solution provided in the answer above.
Here is 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
)
);
}
Related
I have this sample TypeScript code that is supposed to deserialize a simple JSON into an instance of class Person and then call foo method on it, but it doesn't work:
class Person {
name!: string;
age!: number;
foo() {
console.log("Hey!");
}
}
fetch("/api/data")
.then(response => {
return response.json() as Promise<Person>;
}).then((data) => {
console.log(data);
data.foo();
});
The output of console show that object is in a proper shape, but it is not recognized as Person:
Object { name: "Peter", age: 44 }
age: 44
name: "Peter"
Thus when it tries to call foo method it fails:
Uncaught (in promise) TypeError: data.foo is not a function
http://127.0.0.1:8000/app.js:14
promise callback* http://127.0.0.1:8000/app.js:12
How can I fix it? Should I use Object.assign or there is another better/native solution?
let x = (<any>Object).assign(Object.create(Person.prototype), data);
x.foo();
Remember, TypeScript is just a way of annotating JavaScript code with type guards. It doesn't do anything extra. For example, saying that the object returned by response.json() should be treated as a Promise<Person> does not mean it will invoke the constructor of your Person class. Rather, you'll just be left with a plain old JavaScript object that has a name and an age.
It looks to me like you'll need to create a constructor for your Person class which can create a new instance of a Person based on an object that matches its interface. Something like this, perhaps?
interface PersonLike {
name: string;
age: string;
}
class Person implements PersonLike {
constructor(data: PersonLike) {
this.name = data.name;
this.age = data.age;
}
name: string;
age: string;
foo() {
console.log("Hey!");
}
}
fetch("/api/data")
.then(response => {
return response.json() as Promise<PersonLike>;
}).then((data) => {
const person = new Person(data);
person.foo();
});
I'd also recommend using a type guard instead of the as keyword, in case the API you're fetching data from changes. Something like this, perhaps:
function isPersonLike(data: any): data is PersonLike {
return typeof data?.name === 'string' && data?.age === 'string';
}
fetch("/api/data")
.then(response => {
return response.json();
}).then((data: unknown) => {
if (isPersonLike(data)) {
const person = new Person(data);
person.foo();
}
});
... is supposed to deserialize a simple JSON into an instance of class Person and then ...
Unfortunately, generic type in TypeScript only works as some kind of model design assistant. It will never be compiled into JavaScript file. Take your "fetch" code for example:
fetch("/api/data")
.then(response => {
return response.json() as Promise<Person>;
}).then((data) => {
console.log(data);
data.foo();
});
After compile the above TypeScript file into JavaScript, we can find the code as Promise<Person> is completely removed:
fetch("/api/data")
.then(function (response) {
return response.json();
}).then(function (data) {
console.log(data);
data.foo();
});
To implement "type safe deserialization", you need to save class/prototype information during serialization. Otherwise, these class/prototype information will be lost.
... or there is another better/native solution? ... BTW, what if a class field has a custom type, so it is an instance of another class?
No, there is no native solution, but you can implement "type safe" serialization/deserialization with some libraries.
I've made an npm module named esserializer to solve this problem automatically: save JavaScript class instance values during serialization, in plain JSON format, together with its class name information. Later on, during the deserialization stage (possibly in another process or on another machine), esserializer can recursively deserialize object instance, with all Class/Property/Method information retained, using the same class definition. For your "fetch" code case, it would look like:
// Node.js server side, serialization happens here.
const ESSerializer = require('esserializer');
router.get('/api/data', (req, res) => {
// ...
res.json(ESSerializer.serialize(anInstanceOfPerson));
});
// Client side, deserialization happens here.
const ESSerializer = require('esserializer');
fetch("/api/data")
.then(response => {
return response.text() as Promise<string>;
}).then((data) => {
const person = ESSerializer.deserialize(data, [Person, CustomType1, CustomType2]);
console.log(person);
person.foo();
});
I am trying to map a Http JSON Response to a Custom Interface in Angular / typescript. I have tried it in several ways but have not made it yet. The JSON object is not correctly mapped to the interface. The map attribute stays "undefined". If I print the data directly, the JSON data is output correctly - the problem is that I don't know how to access it. Here is my code:
export interface IMap<T> {
map: Map<string, Array<T>>;
}
The JSON answer looks like this. It is Map< String,List< ? >> in Java.
{
"somenumbers": [
20,
40
],
"somemorenumbers": [
71,
111
]
}
Now I tried to map it the following way:
public getValues(
paramList: Array<string>
): Observable<IMap<any>> {
const url = `url`;
let params = new HttpParams();
for (let s of paramList) {
params = params.append("params", s);
}
return this.http.get<IMap<any>>(url, { params });
}
In the configservice I subscribe to the Method. How do I map the Response correctly so that the attribute map in data isn't undefined and can be accessed correctly?
this.configService
.getValues(["somenumbers", "somemorenumbers"])
.subscribe((data: IMap<any>) => {
//outputs the JSON Data as Object{somenumbers: Array(2), somemorenumbers: Array(2), map: Map(0)}
console.error(data);
console.error(data.map);//map is undefined => ERROR
});
As you can see the map attribute is undefined. It is just a "map: Map(0)". Now... - How do I get the JSON stuff into the export interface? The map attribute should be filled with the associated values.
I appreciate any help! :)
If I understood correctly you're expecting that by adding <IMap<any>> to the get call it will then return you the response mapped to IMap. It doesn't, check this issue.
What you can do instead is use rxjs map to map the response yourself like so:
return this.http.get<IMap<any>>(url, { params }).pipe(
map((response) => {
// map the response here
})
);
I realized that I actually don't need the export interface and changed the code to the following. It took a while for me to get that x.y is in ts the same as x["y"]. Via response[parameter] I can access the attributes of the response Object dynamically - exactly what I needed.
public getValues(
paramList: Array<string>
): Observable<Map<string, Array<any>>> {
const url = `url`;
let params = new HttpParams();
for (let s of paramList) {
params = params.append("params", s);
}
return this.http
.get<any>(url, {
params
})
.pipe(
map(response => {
let toReturn = new Map<string, any[]>();
for (let parameter of paramList) {
toReturn.set(parameter, response[parameter]);
}
return toReturn;
})
);
}
The mapping works now! The JSON answer is still the same as in the question above.
this.configService
.getValues(["somenumbers", "somemorenumbers"])
.subscribe((data: Map<string, any[]>) => {
console.error(data);
});
Thanks for the help and links #M Mansour !
games json response
I originally had this piece of code
this.gameService.getAll()
.pipe(map(data => data['hydra:member']))
.subscribe( (games: Game[]) => this.games = games );
but if I want to retrieve more properties from the json response someone told me to do this
this.gameService.getAll()
.pipe(map(data => data['hydra:member']))
.subscribe(result => [result["hydra:member"], result['hydra:totalItems']]);
however how do you add the following to the above code:
(games: Game[]) => this.games = games );
and map totalItems to a variable.
with this line: pipe(map(data => data['hydra:member'])), it will only contain data from hydra:member.
Is this.games contain all data from API or the hydra:member?
try this:
this.gameService.getAll().subscribe((games: Game[]) => {
this.games = games;
this.totalItems = games['hydra:totalItems']
});
I would try defining my payload (the object I plan to return from the call) and fill that object out using type safety to help me out.
Something like this.
// you can just add more properties later if you like
export interface IGamesGetAllResponseObject {
games: any[]; // or better yet define the game object so it isn't any
totalGames: number;
}
// now define a function that will map the response to the intended object
export mapGamesGetAllToReponse(data): IGamesGetAllResponseObject {
return {
games: data['hydra:member'],
totalGames: data['hydra:totalItems'],
};
}
...
//then use it like this
this.gameService.getAll()
.pipe(map(mapGamesGetAllToReponse))
.subscribe( (result: IGamesGetAllResponseObject) => {
this.games = result.games;
this.totalGames = result.totalGames;
});
I haven't checked all my syntax there 100% but it should be very close to a solution for you.
I would also consider doing all that mapping in the service itself, rather than where you are subscribing. By doing that, you can contain the logic about what data you want and how to map it to the service, and the component just requests what it wants.
you can get multi property from the json response by call same property so that the above code will be :
this.gameService.getAll().pipe(map(result =>
{
this.games = result["hydra:member"] ;
this.totalItems = result['hydra:totalItems'];
}
)).subscribe();
and then call 'this.games' and 'this.totalItems' inline subscribe block.
I am handling Http result in a reducer function of an Observable. While a type of the parameter jwt is set as { id: string, auth_token: string, expires_in }, the jwt argument turns out to be a string. I thought TypeScript does parsing automatically. Do I have to do JSON.parse(JSON.stringify(jwt)) by myself?
.mergeMap((jwt: { id: string, auth_token: string, expires_in }) => {})
Type checking external code
There is no relationship between the TypeScript source code and the JavaScript outputs that gets executed at run-time. TypeScript is only effective at catching compile-time errors if the compiled types match the run-time types.
Normally, this isn't a problem. But in scenarios where you call out to external code (i.e. AJAX call to fetch data from the server), there is no guarantee that the response will be the type you expect. So you must be cautious in these scenarios.
Your specific example
I suspect that your code has a variable jwt with type any and you just assigned the type to { id: string, auth_token: string, expires_in } when in fact, jwt was of type string as far as javascript is concerned.
In this case, you already found your solution, JSON.parse(str). This converts the json string into a javascript object.
Now that you have an object, you can use duck typing to infer the run-time type and let typescript know about the type at compile-time via type guards.
Solution
function isDate(obj: any): obj is Date {
return typeof obj === 'object' && 'toISOString' in obj;
}
function isString(obj: any): obj is string {
return typeof obj === 'string';
}
interface JWT {
id: string;
auth_token: string;
expires_in: Date;
}
function isJwt(obj: any): obj is JWT {
const o = obj as JWT;
return o !== null
&& typeof o === 'object'
&& isString(o.id)
&& isString(o.auth_token)
&& isDate(o.expires_in);
}
function print(jwt: any) {
if (typeof jwt === 'string') {
try {
jwt = JSON.parse(jwt);
} catch (e) {
console.error(`String is not JSON: ${jwt}`);
}
}
if (isJwt(jwt)) {
console.log(`Found jwt: ${jwt.id} ${jwt.auth_token} ${jwt.expires_in}`);
} else {
console.error(`Object is not of type jwt: ${jwt}`);
}
}
print(42);
print('failing');
print(null);
print(undefined);
print({});
print({ id: 'id01', auth_token: 'token01', expires_in: new Date(2018, 11, 25) });
Playground
Try running that code on the TS Playground to see how it inspects the object at run-time.
If the jwt(JSON) object is retrieved with Http from HttpModule #angular/http you have to parse it to JSON
e.g.:
import { Http } from '#angular/http';
....
constructor(
private http: Http
...
) {}
this.http.get(url)
.map((res: any) => {
return res.json();
}).subscribe( (jwt: any) => {
//you got jwt in JSON format
});
If you use HttpClient from HttpClientModule #angular/common/http (Angular > 4.3.x) you do not need to parse the received data because it is already done.
import { HttpClient } from '#angular/common/http';
....
constructor(
private http: HttpClient
...
) {}
this.http.get<any>(url)
.subscribe((jwt: any) => {
//you got jwt in JSON format
})
More info in this answer
I have an issue while I try to cast a json response to object, all the properties of my object are string is that normal ?
Here is my ajax request :
public getSingle = (keys: any[]): Observable<Badge> => {
return this._http.get(this.actionUrl + this.getKeysUrl(keys))
.map((response: Response) => response.json() as Badge )
.catch(this.handleError);
}
Here is my badge model :
export interface Badge {
badgeNumber: number;
authorizationLevel: number;
endOfValidity: Date;
}
And here is where I call the service function and I'm facing the issue :
this._badgeService.getSingle(this.ids).subscribe(
(badge: Badge) => {
console.log(typeof(badge.endOfValidity)); // <-- returning string and not Date
},
error => console.log(error);
});
Thats kinda tricky to explain:
Date is a class, this means that values of type Date need to be created through a constructor call. In other words, create a class instance with new Date(...).
The Response.json method will only return an object in JSON format, and such doesnt contain an instance of any class, only maps of key:property.
So what you need to do, is to manually convert the value returned from .json() to a Base object. This can be done as follows:
public getSingle = (keys: any[]): Observable<Badge> => {
return this._http.get(this.actionUrl + this.getKeysUrl(keys))
.map(r => r.json())
.map(v => <Badge>{
badgeNumber: v.badgeNumber,
authorizationLevel: v.authorizationLevel,
endOfValidity: new Date(v.endOfValidity)
// preferably this string should be in ISO-8601 format
})
//the mapping step can be done in other ways most likely
.catch(this.handleError);
}