Lab 19: Signal Store

📖 Resources

• Signal Store Documentation
• @ngrx/signals Guide

🚀 Starter Code

step-18-album-wholesale-v21-post-signal-form

In this lab, you’ll implement centralized state management using NgRx SignalStore. You’ll install @ngrx/signals, define a full state interface, create computed values, and implement all CRUD operations as async methods using rxMethod.

📝 Instructions

Step 1: Install @ngrx/signals

npm install @ngrx/signals

Step 2: Define the State Interface

Create src/app/store/album.store.ts. Start by defining a complete state interface — don’t leave out fields you’ll need later:

import { Album } from '../model/album.model';

interface AlbumState {
  albums: Album[];
  selectedAlbum: Album | null;
  loading: boolean;
  loaded: boolean;
  error: string | null;
}

const initialState: AlbumState = {
  albums: [],
  selectedAlbum: null,
  loading: false,
  loaded: false,
  error: null
};

loaded lets components know the first fetch is done. error holds the last error message. selectedAlbum tracks the album currently open in a dialog or detail view.

Step 3: Create the Store with Computed Values

import { computed } from '@angular/core';
import { signalStore, withState, withComputed, withMethods, patchState } from '@ngrx/signals';

export const AlbumStore = signalStore(
  { providedIn: 'root' },

  withState(initialState),

  withComputed((store) => ({
    albumCount: computed(() => store.albums().length),
    hasAlbums: computed(() => store.albums().length > 0),
    isLoading: computed(() => store.loading()),
    isLoaded: computed(() => store.loaded())
  })),
);

withComputed receives the store slice — use computed() to derive reactive values from signals.

Step 4: Add Methods — Load and Add

Add withMethods after withComputed. Inject the service via the function signature:

import { inject } from '@angular/core';
import { rxMethod } from '@ngrx/signals/rxjs-interop';
import { pipe, switchMap, tap } from 'rxjs';
import { AlbumService } from '../services/album.service';

withMethods((store, albumService = inject(AlbumService)) => ({

  loadAlbums: rxMethod<void>(
    pipe(
      tap(() => patchState(store, { loading: true, error: null })),
      switchMap(() => albumService.findAll()),
      tap({
        next: (albums) => patchState(store, { albums, loading: false, loaded: true }),
        error: (error) => patchState(store, { error: error.message, loading: false })
      })
    )
  ),

  addAlbum: rxMethod<Album>(
    pipe(
      tap(() => patchState(store, { loading: true })),
      switchMap((album) => albumService.save(album)),
      tap({
        next: (newAlbum) => patchState(store, {
          albums: [...store.albums(), newAlbum],
          loading: false
        }),
        error: (error) => patchState(store, { error: error.message, loading: false })
      })
    )
  ),

}))

switchMap vs concatMap

switchMap cancels any in-flight request when a new one arrives. This is correct for load and add — if the user triggers the action twice, only the last matters.

For delete, you will use concatMap instead — deletes must complete in order. Cancelling a delete mid-flight could leave the server and the UI out of sync.

Step 5: Add Update and Delete Methods

import { concatMap, finalize, map } from 'rxjs';

// inside withMethods, alongside loadAlbums and addAlbum:

updateAlbum: rxMethod<Album>(
  pipe(
    tap(() => patchState(store, { loading: true })),
    switchMap((album) => albumService.update(album)),
    tap({
      next: (updatedAlbum) => {
        const albums = store.albums().map(a =>
          a.id === updatedAlbum.id ? updatedAlbum : a
        );
        patchState(store, { albums, loading: false });
      },
      error: (error) => patchState(store, { error: error.message, loading: false })
    })
  )
),

deleteAlbum: rxMethod<number>(
  pipe(
    tap(() => patchState(store, { loading: true, error: null })),
    concatMap((id) =>
      albumService.delete(id).pipe(
        map(() => id),
        finalize(() => patchState(store, { loading: false }))
      )
    ),
    tap({
      next: (id) => {
        patchState(store, { albums: store.albums().filter(a => a.id !== id) });
      },
      error: (error) => patchState(store, { error: error?.message ?? 'Delete failed' })
    })
  )
),

finalize runs when the inner observable completes or errors — useful to always reset loading, even on failure.

Step 6: Add Synchronous Methods

Not every method needs rxMethod. Simple state mutations are plain functions:

selectAlbum(album: Album | null) {
  patchState(store, { selectedAlbum: album });
},

clearError() {
  patchState(store, { error: null });
}

These are called directly — no observable, no pipe, no tap.

Step 7: Use the Store in a Component

Inject the store and expose its signals directly as component properties:

import { Component, inject } from '@angular/core';
import { AlbumStore } from '../../../store/album.store';

export class AlbumListComponent {
  private albumStore = inject(AlbumStore);

  // Expose signals — no need to call them here, templates call them
  albums = this.albumStore.albums;
  loading = this.albumStore.loading;
  albumCount = this.albumStore.albumCount;

  constructor() {
    this.albumStore.loadAlbums();
  }

  addAlbum(album: Album) {
    this.albumStore.addAlbum(album);
  }

  deleteAlbum(id: number) {
    this.albumStore.deleteAlbum(id);
  }
}

Template:

@if (loading()) {
  <p>Loading...</p>
}

<p>{{ albumCount() }} albums</p>

@for (album of albums(); track album.id) {
  <app-album-card
    [album]="album"
    (delete)="deleteAlbum(album.id)"
  />
}

Step 8: Trigger addAlbum from a Dialog

The add dialog injects the store directly and calls addAlbum when a user picks an album:

export class AddComponent {
  private albumStore = inject(AlbumStore);
  private dialogRef = inject(MatDialog);

  // Albums already in the store (to filter duplicates)
  albums = this.albumStore.albums;

  makeItAvailable(album: Album) {
    this.albumStore.addAlbum(album);  // store handles save + state update
    this.dialogRef.closeAll();
  }
}

This is the key SignalStore benefit: any component injects the same singleton store — no prop drilling, no @Output chains to the parent.

🧩 Complete Store Reference

import { computed, inject } from '@angular/core';
import { patchState, signalStore, withComputed, withMethods, withState } from '@ngrx/signals';
import { rxMethod } from '@ngrx/signals/rxjs-interop';
import { concatMap, finalize, map, pipe, switchMap, tap } from 'rxjs';
import { AlbumService } from '../services/album.service';
import { Album } from '../model/album.model';

interface AlbumState {
  albums: Album[];
  selectedAlbum: Album | null;
  loading: boolean;
  loaded: boolean;
  error: string | null;
}

const initialState: AlbumState = {
  albums: [],
  selectedAlbum: null,
  loading: false,
  loaded: false,
  error: null
};

export const AlbumStore = signalStore(
  { providedIn: 'root' },
  withState(initialState),

  withComputed((store) => ({
    albumCount: computed(() => store.albums().length),
    hasAlbums: computed(() => store.albums().length > 0),
    isLoading: computed(() => store.loading()),
    isLoaded: computed(() => store.loaded())
  })),

  withMethods((store, albumService = inject(AlbumService)) => ({

    loadAlbums: rxMethod<void>(
      pipe(
        tap(() => patchState(store, { loading: true, error: null })),
        switchMap(() => albumService.findAll()),
        tap({
          next: (albums) => patchState(store, { albums, loading: false, loaded: true }),
          error: (error) => patchState(store, { error: error.message, loading: false })
        })
      )
    ),

    addAlbum: rxMethod<Album>(
      pipe(
        tap(() => patchState(store, { loading: true })),
        switchMap((album) => albumService.save(album)),
        tap({
          next: (newAlbum) => patchState(store, {
            albums: [...store.albums(), newAlbum],
            loading: false
          }),
          error: (error) => patchState(store, { error: error.message, loading: false })
        })
      )
    ),

    updateAlbum: rxMethod<Album>(
      pipe(
        tap(() => patchState(store, { loading: true })),
        switchMap((album) => albumService.update(album)),
        tap({
          next: (updatedAlbum) => {
            const albums = store.albums().map(a =>
              a.id === updatedAlbum.id ? updatedAlbum : a
            );
            patchState(store, { albums, loading: false });
          },
          error: (error) => patchState(store, { error: error.message, loading: false })
        })
      )
    ),

    deleteAlbum: rxMethod<number>(
      pipe(
        tap(() => patchState(store, { loading: true, error: null })),
        concatMap((id) =>
          albumService.delete(id).pipe(
            map(() => id),
            finalize(() => patchState(store, { loading: false }))
          )
        ),
        tap({
          next: (id) => {
            patchState(store, { albums: store.albums().filter(a => a.id !== id) });
          },
          error: (error) => patchState(store, { error: error?.message ?? 'Delete failed' })
        })
      )
    ),

    selectAlbum(album: Album | null) {
      patchState(store, { selectedAlbum: album });
    },

    clearError() {
      patchState(store, { error: null });
    }
  }))
);