Injecting service for another service - javascript

I have few levels of services calling each other, i.e. a ComponentService that uses a DataService that uses an ErrorService.
Now, one of the components services, needs to specify that the ErrorService instance used by the DataService should be of e.g. SpecialErrorService type. - and it does not use the ErrorService or the SpecialErrorService directly.
How can I instruct the data service to inject the correct ErrorService type when instantiating? (Note that I want this behavour only for a specific ComponentService, not as a general case)
#Injectable()
export class SpecialComponentService {
constructor(private _dataService: DataService){}
log() {
//expecting this to log: I'm a special error service
this._dataService.log();
}
}
#Injectable()
export class RegularComponentService {
constructor(private _dataService: DataService){}
log() {
//expecting this to log: I'm a regularerror service
this._dataService.log();
}
}
#Injectable()
export class DataService {
constructor(private _errorService: ErrorService){}
log() {
this._errorService.log();
}
}
#Injectable()
export class ErrorService {
log(){
console.log("I'm a regular error service");
}
}
#Injectable()
export class SpecialErrorService extends ErrorService {
log(){
console.log("I'm a special error service");
}
}

When providing the service you can substitute it by a special service.
For example if you use it within a component, you can provide it like this:
{ provide: ErrorService, useClass: SpecialErrorService }
PS: I wanted to post this as comment but I'm not allowed to. Says I need a 50 reputation...

Related

Angular. How to switch component depending on service's actions

Lets say I have 2 components, aComponent and bComponent. I have them redered inside the AppComponent
<app-a>
<app-b>
And I have service myService that has method .trigger().
What I want is to show only aComponent, but whenever I call myService.trigger() from another part of code, it would switch and show bComponent. That's perfect implementation that I can't reach.
Question is: Is it possible to do so? And if not what is the best closest solution.
The only working solution I got:
I added .trigger() inside AppComponent
export class AppComponent {
title = 'spa';
show: boolean = false;
trigger() {
this.show = true;
}
}
And rendered components like so:
<div *ngIf="!show; else show">
<app-a></app-a>
</div>
<ng-template #show>
<app-b></app-b>
</ng-template>
Then whenever I want to trigger switching, I add instance of the app to the constructor and call it's method:
export class AnotherComponent implements OnInit {
constructor(
private app: AppComponent
) {}
ngOnInit(): void {
this.app.trigger();
}
}
Even though it's working pretty good, I myself see that it's a dirty solution. Components are not intended to be used inside another components, but Services are.
You can use Subject from rxjs library for that.
In your service file:
// a-service.service.ts
import { Injectable } from '#angular/core';
import { Subject } from 'rxjs';
#Injectable({ providedIn: 'root' })
export class AService {
private subject = new Subject<any>();
trigger(state: boolean) {
this.subject.next(state);
}
getTrigger(): Subject<any> {
return this.subject;
}
}
and in your AppComponent:
// app.component.ts
...
private show = false;
constructor (private aService: AService) { }
ngOnInit() {
this.aService.getTrigger().subscribe(state => {
this.show = state;
});
}
the template can be as you provided - it's fine:
<div *ngIf="!show; else show">
<app-a></app-a>
</div>
<ng-template #show>
<app-b></app-b>
</ng-template>
And if you want to trigger from another component, you do it like this:
// another.component.ts
...
constructor (private aService: AService) { }
ngOnInit() {
this.aService.trigger(true);
}
One way to communicate between different components and services which aren't directly related, is via 'Subjects'.
You can try to create a subject and pass in values to it from myService.trigger(). And you can subscribe to that subject from whichever component you want to access that trigger data.

Rxjs : prevent pushing data to subjects from outisde the service

Within my anguular app , i ve this service :
#Injectable()
export class myService{
myBehaviouSubject= new BehaviorSubject("");
setData(){
this.myBehaviouSubject.next("123");
}
}
Inside my app.component , i m able to get the value , but i want to keep it readonly or editable only inside the service itself , i want to prevent to push any data from component (.next('DATA'))
#Component({
})
export class AppComponent implements OnInit {
constructor(public myService : MyService) { }
getData(){
// GET VALUE
this.myService.myBehaviouSubject.value
}
unwantedMethodToSetValue(){
// SET VALUE -> i want to prevent this
this.myService.myBehaviouSubject.next("unwanted value")
}
}
Suggestions ?
You can keep the observable inside service only by declaring it as private field of a class.
#Injectable()
export class myService {
private myBehaviouSubject = new BehaviorSubject("");
// Use this observable inside the app component class.
myBehaviouSubjectObservable = myBehaviouSubject.asObservable();
setData() {
this.myBehaviouSubject.next("123");
}
}
#Component({
})
export class AppComponent implements OnInit {
constructor(public myService: MyService) {}
getData() {
// You can subscribe to observable and can get value here
this.myService.myBehaviouSubjectObservable.subscribe((value) => {
console.log(value);
})
}
unwantedMethodToSetValue() {
// SET VALUE -> you cannot do this here now.
this.myService.myBehaviouSubject.next("unwanted value")
}
}
Use property access modifiers:
#Injectable()
export class MyService{
private myValueSubject: BehaviorSubject<string> = new BehaviorSubject<string>("");
public readonly myValueObservable: Observable<string> = this.myValueSubject.asObservable();
public setData() {
this.myValueSubject.next("123");
}
public getData(): string {
return this.myValueSubject.value;
}
}
Instances of MyService will not have a publicly accessible subject.
I usually try to avoid a method like getData, favoring subscriptions to the related observable. If I ever find myself writing those kinds of methods, it's a warning flag to re-evaluate my architecture. If you just want to store a value and get/set it with methods, use a plain old private property. The entire purpose of the subject is defeated if you are only ever getting the value through a method like getData()
Check out the documentation for typescript classes, which discusses access modifiers: https://www.typescriptlang.org/docs/handbook/classes.html
The traditional answer : If you return the Subject as an observable, you disallow .next() calls.
But in your case, you also want direct access to the current value without subscribing, so you could add a getter for that too.
#Injectable()
export class myService{
private readonly myBehaviouSubject = new BehaviorSubject("");
setData(){
this.myBehaviouSubject.next("123");
}
public get myObservable$(): Observable<string>{
return this.myBehaviourSubject;
}
public get currentValue(): string{
return this.myBehaviourSubject.value;
}
}
https://stackblitz.com/edit/angular-protected-rxjs-subject
in this solution which I hope meet you needs:
be aware that there is no subscription
fetching updates handled manually
Property 'myBehaviourSubject' is private and only accessible
within class 'TestService'.

angular: How to mock extends class in unit test

I've a injectable service (EntityApi) which extends a class (BaseApi). In my spec I like to mock the BaseApi with BaseApiStub. But it vain. Always calling the EntityApi.
// class
export class BaseApi { // want to mock BaseApi
constructor(injector: Injector) {
console.log("Should not be here...");
}
}
// service
#Injectable()
export class EntityApi extends BaseApi {
constructor(injector: Injector) {
super(injector, "entity");
}
}
// component
#Component({
selector: 'rt-entity-list',
templateUrl: './entity-list.component.html',
})
export class EntityListComponent {
api: any;
constructor(public entityApi: EntityApi) {
this.api = entityApi;
}
}
// mock api
export class BaseApiStub { //mocked api
constructor() {
console.log("You are on track!!")
}
get() { }
}
// spec
describe('EntityListComponent', () => {
let component: EntityListComponent;
let fixture: ComponentFixture<EntityListComponent>;
beforeEach(async(() => {
TestBed.configureTestingModule({
declarations: [EntityListComponent],
providers: [ { provide: BaseApi, useClass: BaseApiStub }, // mocked class.
],
schemas: [NO_ERRORS_SCHEMA]
}).compileComponents();
beforeEach(() => {
fixture = TestBed.createComponent(EntityListComponent);
component = fixture.componentInstance;
fixture.detectChanges();
});
it('should create', () => {
expect(component).toBeTruthy();
});
});
Expected Behavior is, while compile component in spec. It should call the BaseApiStub, instead it is calling BaseApi. I've seen a solution as below. But no luck.
export class BaseApiStub extends BaseApi { }
Test Code: stackblitz Check the console. I expect the You are
on track!! log but received as Should not be here...
Not able to progress further. Can someone correct my mistake please.
What you are trying to do does not work. Dependency injection and class inheritance are not directly related. This means you cannot switch out the base class of your service like this.
As I see it you have two ways on how to do this.
Option 1:
Instead of mocking your BaseApi and providing the mock in your test you need to mock your EntityApi and provide this mock in your test.
Option 2:
Instead of letting your EntityApi extend from BaseApi, you could keep BaseApi a simple service and provide it as a dependency.
Instead of
class EntityApi extends BaseApi {
constructor(private injector: Injector) {
you do
class EntityApi {
constructor(private api: BaseApi) {
If you setup your EntityApi like this, it does not extend from BaseApi, but rather has it as a dependency. Then you can create a mock of the BaseApi and provide it like you did in your test.
Edit
Regarding your comment:
Since I should be using methods from BaseApi I cannot go without extends.
This is not true. Let's say the BaseApi has a method foo() that you want to use. When you extend your baseclass, the usage might look like this:
class EntityApi extends BaseApi {
constructor(private injector: Injector) {}
exampleMethod() {
this.foo();
}
}
If you just have the dependency you can still call the method like this:
class EntityApi {
constructor(private api: BaseApi) {}
exampleMethod() {
this.api.foo();
}
}
You don't need to extend from BaseApi in order to call methods on it.
In case you need to mock a method of a parent class (e.g for Directive) you can do that through the stub extension of the tested class.
spyObject = {
methodToSpyOn(){}
};
#Directive({selector: '[myDirective]'})
class MyStubDirective extends MyDirective {
parentMethodToMock() {
return spyObject.methodToSpyOn();
}
}
spyOn(spyObject, 'methodToSpyOn').and.returnValue(true);
This approach is usually needed if your class has the parent method calls in constructor

Angular 4 Singleton Services

I'm trying to create a service to share the data between two components. I injected the service into root module to make it accessible throughout the application by doing DI into the root module provider. My code looks roughly like this.
Service
#Injectable(){
export class ForumService{
forum: any;
setForum(object){
this.forum = object;
}
getForum(){
return this.forum;
}
}
Root Module
.......
import { ForumService } from 'forumservice';
.......
#NgModule({
declarations: [.....],
imports: [.....],
providers: [....., ForumService],
bootstrap: [AppComponent]
})
export class AppModule{}
Component One
//A bunch of import statements
import { ForumService } from 'forumservice'; //Without this Angular throws a compilation error
#Component({
selector: 'app-general-discussion',
templateUrl: './general-discussion.component.html',
styleUrls: ['./general-discussion.component.css'],
providers: [GeneralDiscussionService] //Not injecting ForumService again
})
export class GeneralDiscussionComponent implements OnInit{
constructor(private forumService: ForumService){}
ngOnInit(){
helperFunction();
}
helperFunction(){
//Get data from backend and set it to the ForumService
this.forumService.forum = data;
console.log(this.forumService.forum); //prints the data, not undefined
}
}
Component Two
//A bunch of import statements
import { ForumService } from 'forumservice'; //Without this Angular throws a compilation error
#Component({
selector: 'app-forum',
templateUrl: './forum.component.html',
styleUrls: ['./forum.component.css'],
providers: []
})
export class ForumComponent implements OnInit {
forumData: any;
constructor(private forumService: ForumService){}
ngOnInit(){
this.forumData = this.forumService.forum; // returns undefined
}
}
Once I navigate from Component One to Component Two I'm expecting "This is a string". However I get undefined. Is it because of the import statements in the component? If I remove that I see a compilation error saying that ForumService is not found.
Instead of using getter and setter, use the object (not primitibe such as string) directly In your components.
Your service
#Injectable(){
export class ForumService{
forum:any = {name:string};
}
Component one
export class GeneralDiscussionComponent implements OnInit{
constructor(private forumService: ForumService){}
ngOnInit(){
this.forumService.forum.name="This is a string";
}
}
Component two
export class ForumComponent implements OnInit {
// forumTitle: string; // do not need this anymore
forum:any; // use the forum.name property in your html
constructor(private forumService: ForumService){}
ngOnInit(){
this.forum = this.forumService.forum; // use the
}
}
I know encapsulating is preferable, and with your current code you are probably encountering some timing problems. But when working with shared data in a service you can two-way bind the variable like above, and your components will be in sync.
EDIT:
Also an important notice, the variable you want to sync between components needs to be an object. instead of forumTitle:string, make it forumTitle:any = {subject:string} or something similar.
Otherwise you need to make your components as listeners for data when data changes in your service.
I'd use BehaviorSubject in this case, should be something like that:
#Injectable(){
export class ForumService{
private _forum: BehaviorSubject<any> = new BehaviorSubject<any>(null);
public forum: Observable<any> = this._forum.asObservable();
setForum(object){
this._forum.next(object);
}
}
Then just bind it in template with async pipe: {{forumService.forum|async}} or subscribe to it.

Global function available through all app Angular2

I have a PermissionService, which provide user roles. At the server-side data will not be uploaded if the user is not corresponds on role. The back-end is written with asp.net web api, which will use attributes to secure data. On upload page will be static upload user roles, the idea is just to show or hide elements on page which depending from user role.
The PermissionsService check avaiable role in its array. There are methods like isSeller(), isManager(). And all what i want is to provide accessibility from each view. For now i have this implementation.
permission.service
import { Injectable } from "#angular/core";
export enum Roles {
Admin,
Manager,
Moderator,
Seller
}
interface IPermissionDictionary {
[key: string]: boolean;
}
#Injectable()
export class PermissionService {
private permissions: IPermissionDictionary = {};
public constructor() {
this.emitPermissions();
}
private emitPermissions(): void {
let selector = document.querySelectorAll("#roles > span");
let availableRoles = Array.from(selector).map(element => element.textContent);
for (let role in Roles) {
if (!/^\d+$/.test(role)) { // for strings types in Roles
this.permissions[role] = availableRoles.indexOf(role) > -1;
}
}
}
public isInRole(role: string): boolean {
return this.permissions[role];
}
public isAdmin() {
return this.isInRole(Roles[Roles.Admin]);
}
public isSeller() {
return this.isInRole(Roles[Roles.Seller]);
}
public isManager() {
return this.isInRole(Roles[Roles.Manager]);
}
public isModerator() {
return this.isInRole(Roles[Roles.Moderator]);
}
}
app.component
import { Component } from "#angular/core";
import { ROUTER_DIRECTIVES } from "#angular/router";
import { PermissionService } from "./share/permission.service";
import { HomeComponent } from "./home/home.component";
import { OrderComponent } from "./order/order.component";
#Component({
selector: "admin-panel",
templateUrl: "../app/app.template.html",
directives: [ROUTER_DIRECTIVES],
precompile: [HomeComponent, OrderComponent]
})
export class AppComponent {
constructor(private permissionService: PermissionService) {
}
}
main.ts
import { bootstrap } from "#angular/platform-browser-dynamic";
import { AppComponent } from "./app.component";
import { APP_ROUTES_PROVIDER } from "./app.routes";
import { HTTP_PROVIDERS } from '#angular/http';
import { PermissionService } from "./share/permission.service";
bootstrap(AppComponent, [APP_ROUTES_PROVIDER, HTTP_PROVIDERS, PermissionService]);
For now to access the method of PermissionService need to inject it in component constructor. And in template is is use like
<div *ngIf="permissionService.isAdmin()">will show if you are admin</div>
But every time to inject my service in each component where i want to use it seems for me strange. And i just want to get access it from every part of my app like:
<div *ngIf="isAdmin()">will show if you are admin</div>
I think the person who asked this question has another version of Angular2 (perhaps a pre-release?), but in the latest version if you need to export a service for all the app you do it in the following way.
First, in your main.ts you must have a class that you bootstrap, like this:
platformBrowserDynamic().bootstrapModule(AppModule);
In this class "AppModule" (or whatever it is in your case), you should be able to add a global service provider in this way:
...
import {GlobalService} from './global-service.service'
#NgModule({
...
providers: [MyGlobalService],
...
})
export class AppModule{ ...}
In this way MyGlobalService is available for all other components.
Hopefully this will be useful to someone :).
Some option could be to create top level super class with the permission methods and then just subclass in view .ts. Not sure if this suits you as you still need to import super class into your components and extend it. It can also violate the "is-a".

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