[Angular 2] Handle Reactive Async opreations in Service

Posted 2020-07-28 Answer1215

When you use ngrx/store and you want to fire a service request. When it sucessfully return the response, you need to dispatch action to tell the store update.

 

So one pattern can be considered to follow is:

import {Http, Headers} from ‘@angular/http‘;
import {Injectable} from ‘@angular/core‘;
import {Store} from ‘@ngrx/store‘;
import {Observable} from "rxjs/Observable";
import ‘rxjs/add/operator/map‘;

import {AppStore} from ‘../models/appstore.model‘;
import {Item} from ‘../models/item.model‘;

const BASE_URL = ‘http://localhost:3000/items/‘;
const HEADER = { headers: new Headers({ ‘Content-Type‘: ‘application/json‘ }) };

@Injectable()
export class ItemsService {
  items: Observable<Array<Item>>;

  constructor(private http: Http, private store: Store<AppStore>) {
    this.items = store.select(‘items‘);
  }

  loadItems() {
    this.http.get(BASE_URL)
      .map(res => res.json())
      .map(payload => ({ type: ‘ADD_ITEMS‘, payload }))
      .subscribe(action => this.store.dispatch(action));
  }

  saveItem(item: Item) {
    return (item.id) ? this.updateItem(item) : this.createItem(item);
  }

  createItem(item: Item) {
     return this.http.post(`${BASE_URL}`, JSON.stringify(item), HEADER)
      .map(res => res.json())
      .do(payload => {
        const action = { type: ‘CREATE_ITEM‘, payload };
        this.store.dispatch(action)
      });
  }

  updateItem(item: Item) {
    return this.http.put(`${BASE_URL}${item.id}`, JSON.stringify(item), HEADER)
      .do(action => this.store.dispatch({ type: ‘UPDATE_ITEM‘, payload: item }));
  }

  deleteItem(item: Item) {
    return this.http.delete(`${BASE_URL}${item.id}`)
      .do(action => this.store.dispatch({ type: ‘DELETE_ITEM‘, payload: item }));
  }
}

 

 

In this ItemService, we get Items from store:

  items: Observable<Array<Item>>;

  constructor(private http: Http, private store: Store<AppStore>) {
    this.items = store.select(‘items‘);
  }

 

To change state, it flows the style that

• Call the backend
• if success generate action
• dispatch the action

 createItem(item: Item) {
     return this.http.post(`${BASE_URL}`, JSON.stringify(item), HEADER)
      .map(res => res.json())
      .do(payload => {
        const action = { type: ‘CREATE_ITEM‘, payload };
        this.store.dispatch(action)
      });
  }

 

In the controller:

  saveItem(item: Item) {
    this.itemsService.saveItem(item)
      .subscribe( (res) => {this.resetItem()},
                  (err) => {console.error(err)},
                 () => {console.info("Completed")});

 

If you notice, in loadItems, I didn‘t‘ use do() to dispatch action and subscribe in controller, instead I subscribe in service, this is because in controller, it doesn‘t expect receive anything from service:

  constructor(private itemsService: ItemsService,
              private gadgetService: GadgetService,
              private store: Store<AppStore>) {
    this.items = itemsService.items;
    itemsService.loadItems();
  }

We base on async pipe to update the dom:

      <items-list [items]="items | async"
        (selected)="selectItem($event)" (deleted)="deleteItem($event)">
      </items-list>

But for createItem, deleteItem, we use do() to dispatch action and subscribe action, this is because we want to confrim weather it successfully updated, then we want to clear the input fields.