I am kind of new to typescript and javascript, and I am having a real hard time figuring out how collections and file io works. I am trying to get data from a json file, which that I am successful in although when I put it into a collection the collection does not have the data.
Here is the code:
In my service class:
private configuration = "../../assets/Configurations/testConfiguration.json";
constructor(private http: HttpClient) {}
getBlogs(blog: string): Observable<IBlogPost[]> {
return this.http.get<IBlogPost[]>(blog);
}
getConfigurations() {
var configurationsData = [];
this.http.get(this.configuration).subscribe(data => {
configurationsData.push(data);
console.log(data);
// This will work and will print all the paths
});
//This will not work and will not print them, like if the collection is empty
configurationsData.forEach(x => console.log(x));
return configurationsData;
}
Where I get my service class injected:
blogs: IBlogPost[] = [];
private blogsPaths: string[] = [];
errorMessage = "";
constructor(private appUtilityService: AppUtilityServices) {}
ngOnInit() {
//This will not work, blogsPaths will not received the full collection as it should
this.blogsPaths = this.appUtilityService.getConfigurations();
this.blogsPaths.forEach(blogPath =>
this.appUtilityService.getBlogs(blogPath).subscribe(
b =>
b.forEach(blog => {
this.blogs.push(blog);
}),
error => (this.errorMessage = <any>error)
)
);
}
testConfiguration.json:
[
"../../assets/BlogPosts/testBlog1.json",
"../../assets/BlogPosts/testBlog2.json"
]
Bonus if you include a good tutorial on how collections work in javascript and how to return them properly
Turns out to be this, yes really...
Here I made it nice:
OnInit:
this.appUtilityService.getConfigurations().subscribe(
b =>
b.forEach(x => {
this.appUtilityService.getBlogs(x).subscribe(
b =>
b.forEach(blog => {
this.blogs.push(blog);
}),
error => (this.errorMessage = <any>error)
);
}),
error => (this.errorMessage = <any>error)
);
AppUtilityService:
getBlogs(blog: string): Observable<IBlogPost[]> {
return this.http.get<IBlogPost[]>(blog);
}
getConfigurations(): Observable<string[]> {
return this.http.get<string[]>(this.configuration);
}
Make it really nice:
ngOnInit() {
this.initializeBlog();
}
private initializeBlog(): void {
this.appUtilityService.getConfigurations().subscribe(
b =>
b.forEach(x => {
this.appUtilityService.getBlogs(x).subscribe(
b =>
b.forEach(blog => {
this.blogs.push(blog);
}),
error => (this.errorMessage = <any>error)
);
}),
error => (this.errorMessage = <any>error)
);
}
Inside getConfigurations, you're invoking an asynchronous http request. So it's normal, that configurationsData is empty outside the subscribe method.
Here, I'm using the powerful of RxJS to simplify the code and avoid to use
Array.push and nested subscribe().
1) Basic async service method to get data
So getConfigurations should return an Observable:
getConfigurations(): Observable<string[]> {
return this.http.get<string[]>(this.configuration);
}
And also getBlogs should return an Observable:
getBlogs(blogsPath: string): Observable<BlogPost[]> {
return this.http.get<BlogPost[]>(blogsPath);
}
Here, to respect Angular best practice, I remove I at the beginning of each interface, so BlogPost.
2) Here is the magic of RxJS
Then, you have another method inside your service to retrieve an Observable of blog posts, which should look like this:
getBlogPosts(): Observable<BlogPost[]> {
return this.getConfigurations().pipe(
mergeAll(),
concatMap(blogsPath => this.getBlogs(blogsPath)),
concatAll(),
toArray()
)
}
Which means, retrieve all collection of blog paths, for each array of paths, for each path, get blog posts, and then return an unique array of all posts.
Finally, inside your component, you call getBlogPosts with a subscription:
ngOnInit() {
this.service.getBlogPosts().subscribe(blogs => {
...do something with your blogs array.
});
}
or even better with async pipe inside your template :
.ts file:
blogs$: Observable<BlogPost[]>;
...
this.blogs$ = this.appService.getBlogPosts();
.html file:
<ul *ngIf="blogs$ | async as blogs">
<li *ngFor="let blog of blogs">
#{{ blog.id }} - {{ blog.title }}
</li>
</ul>
Check my full demonstration of this RxJS alternative on Stackbliz.
Recommended read on medium from Tomas Trajan
Related
I'm using and learning Angular 15 and I have this injectable class which creates an NgRx effect to store data in a firebase database but it throws undefined.
constructor(private actions$: Actions, private http: HttpClient) {}
fetchRecipes = createEffect((): any => {
this.actions$.pipe(
ofType(RecipesActions.FETCH_RECIPES),
switchMap(() => {
return this.http.get<Recipe[]>
(
'https://recipebook-re-default-rtdb.europe-west1.firebasedatabase.app/recipes.json',
)
}),
map(recipes => {
return recipes.map(recipe => {
return {
...recipe,
ingredients: recipe.ingredients ? recipe.ingredients : []
};
});
}),
map(recipes => {
return new RecipesActions.SetRecipes(recipes);
})
);
});
I'm a very-beginner in angular and I did this effect following a course, maybe the course is a bit outdated and something is deprecated but I can not figure it out.
EDIT: Code on GitHub (can't get stacblitz to work sorry)
I feel so dumb, the problem was that I didn't return the this.actions$.pipe() so it didn't returned anything after all...
constructor(private actions$: Actions, private http: HttpClient) {}
fetchRecipes = createEffect((): any => {
return this.actions$.pipe(...)
});
I have the following function that traverse the tree-like object and it working fine so far.
const traverse = async (menuInputs: MenuInput[], parent: Menu = null) => {
for (const input of menuInputs) {
const entity = toEntity(input, parent);
const parentMenu = await this.menuService.create(entity).toPromise();
if (isEmpty(input.children)) {
continue;
}
await traverse(input.children, parentMenu);
}
};
My question is how can i invoke method this.menuService.create(entity) that is actually return an Observable<Menu> without convert it to Promise, are there any RxJS way of doing this ?
I've got something like this for recursive observable calls using the HttpService. You can probably work with something similar.
#Injectable()
export class CharacterReaderApiService implements CharacterReader {
private characters: SwapiCharacter[] = [];
constructor(private readonly http: HttpService) {}
async getCharacters(): Promise<Character[]> {
console.log('Querying the API for character data...');
return this.callUrl('https://swapi.dev/api/people')
.pipe(
map((data) => {
return data.map(this.mapPerson);
}),
tap(async (data) =>
promises.writeFile(join(process.cwd(), characterFile), JSON.stringify(data)),
),
)
.toPromise();
}
private callUrl(url: string): Observable<SwapiCharacter[]> {
return this.http.get<SwapiResponse>(url).pipe(
map((resp) => resp.data),
mergeMap((data) => {
this.characters.push(...data.results);
return iif(() => data.next !== null, this.callUrl(data.next), of(this.characters));
}),
);
}
private mapPerson(data: SwapiCharacter): Character {
return {
name: data.name,
hairColor: data.hair_color,
eyeColor: data.eye_color,
gender: data.gender,
height: data.height,
};
}
}
The important thing is keeping a running array of the values so that they can be referenced later on.
By using mergeMap with iif we're able to recursively call observables and work with the result as necessary. If you don't like the idea of a class variable for it, you could make the running array a part of the callUrl (or similar) method's parameters and pass it on as needed.
I'd strive to change toEntity() and menuService.create() to receive the list of children rather than the parent so I could use forkJoin:
const buildMenu = (input: MenuInput) =>
forkJoin(
input.children.map(childInput => buildMenu(childInput, menu))
).pipe(
flatMap(childMenus => this.menuService.create(toEntity(input, childMenus)))
);
I have a simple app on Angular/rxjs/Ngrx which requests list of default films from the api.
component.ts
export class MoviesComponent implements OnInit {
private movies$: Observable<{}> =
this.store.select(fromRoot.getMoviesState);
private films = [];
constructor(public store: Store<fromRoot.State>) {}
ngOnInit() {
this.store.dispatch(new MoviesApi.RequestMovies());
this.movies$.subscribe(film => this.films.push(film));
console.log(this.films)
}
effects.ts
#Effect()
requestMovies$: Observable<MoviesApi.MoviesApiAction> = this.actions$
.pipe(
ofType(MoviesApi.REQUEST_MOVIES),
switchMap(actions => this.MoviesApiServ.getDefaultMoviesList()
.pipe(
mergeMap(movies => of(new MoviesApi.RecieveMovies(movies))),
catchError(err => {
console.log('err', err);
return of(new MoviesApi.RequestFailed(err));
})
)
)
);
service.ts
export class MoviesApiService {
private moviesList = [];
constructor(private http: HttpClient) { }
public getDefaultMoviesList(): Observable<{}> {
DEFAULT_MOVIES.map(movie => this.getMovieByTitle(movie).subscribe(item => this.moviesList.push(item)));
return from(this.moviesList);
}
public getMovieByTitle(movieTitle: string): Observable<{}> {
return this.http.get<{}>(this.buildRequestUrl(movieTitle))
.pipe(retry(3),
catchError(this.handleError)
);
}
}
DEFAULT_MOVIES is just array with titles.
So my getDefaultMoviesList method is not sending data. But if I replace this.moviesList to hardcoced array of values it works as expected.
What I'm doing wrong?
UPD
I wanted to loop over the default list of films, then call for each film getMovieByTitle and collect them in array and send as Observable. Is there any better solution?
1) You should probably move this line to the service contructor, otherwise you will push a second array of default movies every time you getDefaultMoviesList:
DEFAULT_MOVIES.map(movie => this.getMovieByTitle(movie).subscribe(item => this.moviesList.push(item)));
2) Actually you should probably merge the output of each http.get:
public getDefaultMoviesList(): Observable<{}> {
return merge(DEFAULT_MOVIES.map(movie => this.http.get<{}>(this.buildRequestUrl(movieTitle))
.pipe(retry(3),
catchError(this.handleError)
)))
}
3) You should actually only do that once and store it in BehaviorSubject not to make new HTTP request on each getDefaultMoviesList
private movies$: BehaviorSubject<any> = new BehaviorSubject<any>();
public getMovies$() {
return this.movies$.mergeMap(movies => {
if (movies) return of(movies);
return merge(DEFAULT_MOVIES.map(movie => this.http.get<{}>(this.buildRequestUrl(movieTitle))
.pipe(retry(3),
catchError(this.handleError)
)))
})
}
4) Your implementation shouldn't work at all since:
public getDefaultMoviesList(): Observable<{}> {
DEFAULT_MOVIES.map(movie => this.getMovieByTitle(movie).subscribe(item =>
this.moviesList.push(item))); // This line will happen after http get completes
return from(this.moviesList); // This line will happen BEFORE the line above
}
So you will always return an Observable of empty array.
5) You shouldn't use map if you don't want to map your array to another one. You should use forEach instead.
map is used like this:
const mappedArray = toMapArray.map(element => someFunction(element));
You can try creating the observable using of operator.
Ex: of(this.moviesList);
One intersting fact to note is that Observable.of([]) will be an empty array when you subscribe to it. Where as when you subscribe to Observable.from([]) you wont get any value.
Observable.of, is a static method on Observable. It creates an Observable for you, that emits value(s) that you specify as argument(s) immediately one after the other, and then emits a complete notification.
I am new to Angular, JS, and observables. I have a typescript class called DataService. I want it to load a list of URLs from a JSON formatted local file, and then have some way to call those URLs (to a handful of REST APIs) and return observables. The problem I am having is my code is not waiting for the config file to be loaded before the REST API functions get called.
I thought I could have the DataService constructor load the configuration file, and then have unique functions for each REST API call, but that isn't working
my code:
export class DataService {
configFile
constructor(private http: HttpClient) {
this.http.get('/assets/restApiUrlListConfig.json').subscribe(config => {
this.configFile = config;
});
}
getUrlFromConfigFile(name: string): string {
...
this returns the URL from the config file
...
}
getUrlAData(): Observable {
return this.http.get( getUrlFromConfigFile('A') )
}
}
My other components have code like this:
export class SomeComponent implements OnInit {
someComponentAData
constructor(private data: DataService) { }
ngOnInit() {
this.data.getUrlAData().subscribe(
data => {
this.someComponentAData = data
}
)
}
I am getting an error that the observable returned from the dataservice is undefined. Which I believe is because the constructor hasn't finished loading the config file, which I think is why the function getUrlAData isn't returning anything.
I feel like I'm not correctly handling these async calls, but I'm at a loss for how to tell my code to :
create the data service object
load the data file before anything else can be done
allow the other functions to be called asyncronously AFTER the config file is loaded
Angular CLI: 6.2.3
Node: 8.12.0
OS: win32 x64
Angular: 6.1.8
Edit 1: attempting to implement suggested solution
My DataService
configFile
configObservable: Observable<any>;
someSubscribeObj
constructor(private http: HttpClient) {
this.someSubscribeObj = this.http.get('/assets/restApiUrlListConfig.json').subscribe(config => {
this.someSubscribeObj = undefined;
this.configFile = config;
});
}
getObsFromConfigFile(name: string): Observable<any> {
//...
if (this.configFile != undefined) {
console.log('this.restApiUrlListConfig[name]',this.configFile[name])
return of(this.configFile[name])
}
else
return of(this.someSubscribeObj.pipe(map(c => c[name])))
//this.configObservable
//...
}
getUrlAData(): Observable<any> {
return this.getObsFromConfigFile('A').pipe(mergeMap(url => this.http.get(url)))
}
My other component:
constructor( private data: DataService ) { }
ngOnInit() {
//this.data.loggedIn.pipe((p) => p);
this.data.getUrlAData().subscribe(
data => {
this.urlAData = data
}
)
}
I was unable to store the "subscribe" into the observable, so I created a generic Any type varable, but at runtime I get a problem with the pipe command:
TypeError: this.someSubscribeObj.pipe is not a function
at DataService.push../src/app/services/data.service.ts.DataService.getObsFromConfigFile
(data.service.ts:67)
at DataService.push../src/app/services/data.service.ts.DataService.getUrlAData
(data.service.ts:74)
Edit 2: the unfortunate workaround
I am currently using two nested subscriptions to get the job done basically
http.get(config_file_url).subscribe(
config => {
http.get( config['A'] ).subscribe( adata => { do things };
http.get config['B'].subscribe( bdata => {do things };
}
)
I feel like I should be able to use a mergeMap of some sort, but I couldn't get them to work as I thought they would.
You need to wait on that async call, I would use a flatmap to get the value out of an observable.
export class DataService {
configFile
configObservable: Observable<any>;
constructor(private http: HttpClient) {
this.configObservable = this.http.get('/assets/restApiUrlListConfig.json').pipe(
map(config => {
this.configObservable = undefined;
this.configFile = config;
return configFile;
})
);
}
getUrlFromConfigFile(name: string): Observable<string> {
...
return of(configFile[name]) if configFile is set else return configObservable.pipe(map(c => c[name]));
...
}
getUrlAData(): Observable<string> {
return this.getUrlFromConfigFile('A').pipe(map(url => this.http.get(url)))
}
}
Basically you want to store the observable and keep using it till it completes, after it completes you can just wrap the config in an observable. The reason for wrapping it is to make the interface consistent, otherwise you have to have an if before every get.
I am developing angular application where I need apply following mechanism:
My view has 2 parts (list of items and detail if selected item). User can click on some item, and next service fetch additional data for that item and show them in detail view. Also I want select first item automatically on start if is available.
Here is my service:
#Injectable()
export class ItemService {
private url: string;
private itemSource = new BehaviorSubject<Item>(null);
selectedItem = this.itemSource.asObservable();
constructor(private http: HttpClient) {
this.url = 'http://localhost:8080/api/item';
}
getItems(): Observable<Item[]> {
let observable = this.http.get<Item[]>(this.url)
.map(items => items.map(item => {
return new Item(item);
}));
return observable;
}
selectItem(item: Item) {
return this.http.get<Item>(this.url + '/' + item.id)
.map(item => new Item(item))
.subscribe(t => this.itemSource.next(t));
}
}
in detail component I am subscribing selected item like this:
ngOnInit() {
this.itemService.selectedItem.subscribe(item => this.selectedItem = item);
}
and following code is from my component where I displayed list of items. I also want set selected item after data are subscribed but my code isn't works. I am iterating items[] property in html template and data are showed, but when I access to this array after I subscribed data I got undefined. Can you please fix my code? Thanks!
public items = [];
constructor(private itemService: ItemService) { }
ngOnInit() {
this.itemService.getItems()
.subscribe(
data => this.items = data,
err => console.log(err),
function () {
console.log('selected data', this.items); // this prints undefined
if (this.items && this.items.length) {
this.itemService.selectedItem(this.items[0])
}
});
}
Your problem is that you are not using an arrow function for the complete callback in your call to subscribe. As you see, you are using arrow functions for next and error.
When you define a new function with function(...) {...} you're creating a new context, and so the this keyword changes its meaning. The difference between arrow function and normal functions (besides being more elegant, in my opinion), is that arrow functions do not define a new context for this, and so the meaning of that keyword is the same as in the context they are defined. So, in your next and error callbacks, this is your component, but in your call to complete, this is, most surely, a reference to window, which does not have an items property, hence the undefined.
Change your code to:
public items = [];
constructor(private itemService: ItemService) { }
ngOnInit() {
this.itemService.getItems()
.subscribe(
data => this.items = data,
err => console.log(err),
() => {
console.log('selected data', this.items); // this prints undefined
if (this.items && this.items.length) {
this.itemService.selectedItem(this.items[0])
}
});
}
I imagine you used the function keyword there because that function had not arguments, but you can express that with the syntax () => expression, or () => {...}
data => this.items = data, after all, is a simpler and more elegant way of writing
(data) => { return this.items = data; }