What is the best approach for retrieving asynchronous data from a service?

Question

What is the best approach for retrieving asynchronous data from a service?

After retrieving data from an HTTP request, I am storing it in an array within the same service.

export class UserService {
    myusers: User[];
    constructor(private http: HttpClient) {}
    getUsers () {
     return this.http.get<User[]>('https://randomuser.me/api/results=5')
    .subscribe( data => { this.myusers = data['results']}); }
}

Despite storing the data, when I console log myusers in component.ts, it shows 'Undefined'.

export class UserComponent implements OnInit {
  constructor(private service: UserService) { }
  ngOnInit() {
    this.service.getUsers();
    console.log(this.service.myusers); //undefined
  }
}

Is there a way to access the this.service.myusers without resorting to storing the data in the component's array instead of the service's myusers array?

angular typescript angular4-httpclient

Answer 1

Answer №1

You have the ability to convert an array into an Observable by using Observable.of.

values=[{id:1,name:"one"},{id:2,name:"two"},{id:3,name:"three"}];

getUsers()
{ 
    if (this.values)
       return Observable.of(this.values);
    else 
        return this.http.get(url).map((response)=>
        this.values=...
        ...);
}

Answer 2

You have the ability to convert an array into an Observable by using Observable.of.

values=[{id:1,name:"one"},{id:2,name:"two"},{id:3,name:"three"}];

getUsers()
{ 
    if (this.values)
       return Observable.of(this.values);
    else 
        return this.http.get(url).map((response)=>
        this.values=...
        ...);
}

Answer 3

Answer №2

When retrieving data from an API, there may be a slight delay, so it's important to have a callback function from your service to indicate when the job is complete.

export class UserService {
    myusers: User[];
    constructor(private http: HttpClient) {}
    getUsers () {
        return this.http.get<User[]>('https://randomuser.me/api/results=5');
    }
    setUsers (users: User[]) {
        this.myusers = users;
    }
}

To call the function, use the following code:

export class UserComponent implements OnInit {
  constructor(private service: UserService) { }
  ngOnInit() {
    this.service.getUsers()
    .subscribe( data => { this.service.setUsers(data); console.log(data); });
  }
}

If this solution doesn't meet your needs, please let me know.

Answer 4

When retrieving data from an API, there may be a slight delay, so it's important to have a callback function from your service to indicate when the job is complete.

export class UserService {
    myusers: User[];
    constructor(private http: HttpClient) {}
    getUsers () {
        return this.http.get<User[]>('https://randomuser.me/api/results=5');
    }
    setUsers (users: User[]) {
        this.myusers = users;
    }
}

To call the function, use the following code:

export class UserComponent implements OnInit {
  constructor(private service: UserService) { }
  ngOnInit() {
    this.service.getUsers()
    .subscribe( data => { this.service.setUsers(data); console.log(data); });
  }
}

If this solution doesn't meet your needs, please let me know.

Answer 5

Answer №3

Here is an example of how your service and component should be structured in Angular4 using TypeScript.

    import {Injectable} from '@angular/core';
    import {Http, Response} from '@angular/http';
    import {Observable} from 'rxjs/Observable';

    @Injectable()

    export class UserService {
        constructor(private http: Http) {}

        getUsers (): Observable<void> {
            const url = 'https://randomuser.me/api/results=5';
            return this.http.get(url).map(
                (res: Response) => {
                  return res.json() as = User[];
                }).catch(
                (error: Response) => {
                    return Observable.throw(error.json());
                });
        }
    }

Below is an example of how the Component should be implemented:

export class UserComponent implements OnInit {
  users: User[] = [];

  constructor(private userService: UserService) { }

  ngOnInit() {
    this.getUsers();
  }

  private getUsers(): void {
       this.userService.getUsers().subscribe(
         (response: User[]) => {
           this.users = response;
           console.log(response); 
        );
    }       
}

Keep in mind that Angular4 is based on TypeScript, so it's best practice to assign types to methods and variables.

Answer 6

Here is an example of how your service and component should be structured in Angular4 using TypeScript.

    import {Injectable} from '@angular/core';
    import {Http, Response} from '@angular/http';
    import {Observable} from 'rxjs/Observable';

    @Injectable()

    export class UserService {
        constructor(private http: Http) {}

        getUsers (): Observable<void> {
            const url = 'https://randomuser.me/api/results=5';
            return this.http.get(url).map(
                (res: Response) => {
                  return res.json() as = User[];
                }).catch(
                (error: Response) => {
                    return Observable.throw(error.json());
                });
        }
    }

Below is an example of how the Component should be implemented:

export class UserComponent implements OnInit {
  users: User[] = [];

  constructor(private userService: UserService) { }

  ngOnInit() {
    this.getUsers();
  }

  private getUsers(): void {
       this.userService.getUsers().subscribe(
         (response: User[]) => {
           this.users = response;
           console.log(response); 
        );
    }       
}

Keep in mind that Angular4 is based on TypeScript, so it's best practice to assign types to methods and variables.

What is the best approach for retrieving asynchronous data from a service?

Answer №1

Answer №2

Answer №3

Similar questions

Error: Missing default export in the imported module "react" according to ESLint

The HTML template remains unchanged unless explicitly triggering detectChanges() with change detection set to onpush

Ways to determine the presence of a value in an array

Retrieve the generic type parameter of an interface implementation

In Angular 6, users need to click twice for anchor scrolling to function properly

Ways to include x-api-key in Angular API request headers

"Error in Visual Studio: Identical global identifier found in Typescript code

Error: Angular encountered an undefined variable when attempting to import 'node_modules/bootstrap/scss/grid'

Tips for resolving the error "Binding element has no default value and initializer provides no value in TypeScript"

Angular NgClass Issue (Unable to bind to 'ngClass' as it is not recognized as a property of 'a')

In Angular 12, the search button's response data does not appear in the template until the button is clicked twice

Can you please explain how to upload an image and save it in the assets folder in Angular

What is the best way to protect an Angular/Spring application using Keycloak?

The 'required' validator in Mongoose seems to be malfunctioning

Tips on preventing Realtime database onWrite trigger function callback from iterating through data that has been altered

Having trouble sending a x-www-form-urlencoded POST request in Angular?

Leveraging Angular Universal Prerendering to fetch content from /static/data.json using the httpClient module

Step-by-step guide on building a mat-table with nested attributes as individual rows

What sets apart gzip from x-gzip content? And how can I decompress x-gzip specifically? zlib appears to be struggling

Guide on injecting a service into a directive within Angular version 13