Make the design contract executable.
The reference implementation uses Angular 16, NgRx Store and Effects, RxJS, typed reactive forms, and OnPush components. The version aligns with the later period of the enterprise work. This newly authored example is a demonstration, not a production dependency recommendation.
Component layerQueue presentation · Editor form · Accessible feedback
State and effectsQuery and selection · Saved records · Request lifecycle
Service boundaryAsynchronous search · Explicit writes · Revision checks
Server state and form state have different jobs.
The store holds saved records and request status. The typed reactive form owns the draft. A save error changes the feedback, not the input values. A successful save returns a revised record and resets the form to that new baseline.
Reads and writes need different concurrency rules.
Search uses switchMap so a newer query replaces an older request. Save uses exhaustMap so repeated clicks cannot submit multiple writes while one is pending. Errors are caught inside each request stream so later actions still work.
A real API integration would replace the mock service behind this boundary. Request types describe the contract; runtime response validation, authorization, idempotency, and revision enforcement still belong at the appropriate client and server boundaries.
Request coordinationeffects.ts
Search cancellation, explicit save concurrency, and recoverable request streams.
import { Injectable, inject } from '@angular/core';
import { Actions, createEffect, ofType } from '@ngrx/effects';
import { catchError, exhaustMap, map, of, switchMap, timer } from 'rxjs';
import { DemoCasesApi } from './demo-api';
import * as Cases from './state';
@Injectable()
export class CasesEffects {
private readonly actions$ = inject(Actions);
private readonly api = inject(DemoCasesApi);
// A new query immediately cancels the old debounce and the old request.
load$ = createEffect(() => this.actions$.pipe(
ofType(Cases.queryChanged),
switchMap(({ query }) => timer(180).pipe(
switchMap(() => this.api.search(query)),
map(items => Cases.loadSucceeded({ items })),
catchError((error: Error) => of(Cases.loadFailed({ message: error.message })))
))
));
// Ignore repeated clicks until this submission settles. Do not auto-retry writes.
save$ = createEffect(() => this.actions$.pipe(
ofType(Cases.saveRequested),
exhaustMap(({ update }) => this.api.update(update).pipe(
map(item => Cases.saveSucceeded({ item })),
catchError((error: Error) => of(Cases.saveFailed({ message: error.message })))
))
));
}
Typed editor and validationeditor.component.ts
A draft stays editable after failure. Required fields reject whitespace-only values.
import { ChangeDetectionStrategy, Component, EventEmitter, Input, OnChanges, Output, SimpleChanges } from '@angular/core';
import { CommonModule } from '@angular/common';
import { AbstractControl, FormControl, FormGroup, ReactiveFormsModule, ValidationErrors } from '@angular/forms';
import { CaseStatus, CaseUpdate, SupplierCase } from './models';
const meaningfulText = (minimum: number) => (control: AbstractControl): ValidationErrors | null =>
String(control.value ?? '').trim().length >= minimum ? null : { meaningfulText: true };
@Component({
selector: 'case-editor', standalone: true, imports: [CommonModule, ReactiveFormsModule],
changeDetection: ChangeDetectionStrategy.OnPush,
template: `
<section class="editor" aria-labelledby="editor-heading">
<div class="editor-heading"><div><p class="micro">CASE DETAILS</p><h2 id="editor-heading" tabindex="-1">{{ item.id }}</h2></div><button type="button" class="secondary" (click)="close.emit()" [disabled]="saving">{{ form.dirty ? 'Discard & close' : 'Close' }}</button></div>
<p class="supplier-name">{{ item.supplier }}</p><p>{{ item.summary }}</p>
<div class="revision">Revision {{ item.revision }} · {{ item.priority }} priority</div>
<form [formGroup]="form" (ngSubmit)="submit()" novalidate>
<fieldset [disabled]="saving">
<label for="case-owner">Action owner</label><input id="case-owner" formControlName="owner" [attr.aria-invalid]="form.controls.owner.invalid && form.controls.owner.touched" aria-describedby="owner-help">
<p id="owner-help" class="field-help" [class.validation]="form.controls.owner.invalid && form.controls.owner.touched">Enter at least 3 non-whitespace characters.</p>
<label for="case-status">Status</label><select id="case-status" formControlName="status"><option>Open</option><option>In review</option><option>Resolved</option></select>
<label for="case-note">Action note</label><textarea id="case-note" rows="4" formControlName="note" [attr.aria-invalid]="form.controls.note.invalid && form.controls.note.touched" aria-describedby="note-help"></textarea>
<p id="note-help" class="field-help" [class.validation]="form.controls.note.invalid && form.controls.note.touched">Describe the next action or decision; at least 12 characters.</p>
<p class="dirty" aria-live="polite">{{ form.dirty ? 'Unsaved changes' : 'No unsaved changes' }}</p>
<div class="editor-actions"><button type="submit" [disabled]="saving || !form.dirty">{{ saving ? 'Saving…' : 'Save changes' }}</button><button type="button" class="secondary" (click)="reset()" [disabled]="saving || !form.dirty">Discard edits</button></div>
</fieldset>
<p class="feedback error" *ngIf="error" role="alert">{{ error }}</p>
<p class="feedback success" *ngIf="notice" role="status">{{ notice }}</p>
</form>
</section>`
})
export class CaseEditorComponent implements OnChanges {
@Input({ required: true }) item!: SupplierCase;
@Input() saving = false;
@Input() error: string | null = null;
@Input() notice: string | null = null;
@Output() save = new EventEmitter<CaseUpdate>();
@Output() close = new EventEmitter<void>();
readonly form = new FormGroup({
owner: new FormControl('', { nonNullable: true, validators: [meaningfulText(3)] }),
status: new FormControl<CaseStatus>('Open', { nonNullable: true }),
note: new FormControl('', { nonNullable: true, validators: [meaningfulText(12)] })
});
ngOnChanges(changes: SimpleChanges): void {
// Failures change only `error`; the user's unsaved form stays untouched.
if (changes['item']) this.reset();
}
reset(): void { this.form.reset({ owner: this.item.owner, status: this.item.status, note: this.item.note }); }
submit(): void {
if (this.saving) return;
this.form.markAllAsTouched();
if (this.form.invalid) return;
this.save.emit({ ...this.form.getRawValue(), id: this.item.id, revision: this.item.revision });
}
}
Actions, reducer, and view modelstate.ts
Saved data and request state are explicit. A selector supplies the presentation model.
import { createAction, createReducer, on, props, createFeatureSelector, createSelector } from '@ngrx/store';
import { CasesState, CaseUpdate, Query, SupplierCase } from './models';
export const queryChanged = createAction('[Cases] Query changed', props<{ query: Query }>());
export const loadSucceeded = createAction('[Cases API] Load succeeded', props<{ items: readonly SupplierCase[] }>());
export const loadFailed = createAction('[Cases API] Load failed', props<{ message: string }>());
export const caseSelected = createAction('[Cases] Selected', props<{ id: string | null }>());
export const saveRequested = createAction('[Case editor] Save requested', props<{ update: CaseUpdate }>());
export const saveSucceeded = createAction('[Cases API] Save succeeded', props<{ item: SupplierCase }>());
export const saveFailed = createAction('[Cases API] Save failed', props<{ message: string }>());
export const initialState: CasesState = {
items: [], query: { term: '', status: 'All' }, selectedId: null,
loading: false, loadError: null, saving: false, saveError: null, notice: null
};
export const casesReducer = createReducer(initialState,
on(queryChanged, (state, { query }) => ({ ...state, query, loading: true, loadError: null, selectedId: null, saveError: null, notice: null })),
on(loadSucceeded, (state, { items }) => ({ ...state, items, loading: false })),
on(loadFailed, (state, { message }) => ({ ...state, items: [], loading: false, loadError: message })),
on(caseSelected, (state, { id }) => ({ ...state, selectedId: id, saveError: null, notice: null })),
on(saveRequested, state => ({ ...state, saving: true, saveError: null, notice: null })),
on(saveSucceeded, (state, { item }) => ({ ...state, saving: false, items: state.items.map(row => row.id === item.id ? item : row), notice: `Saved ${item.id}. Revision ${item.revision}.` })),
on(saveFailed, (state, { message }) => ({ ...state, saving: false, saveError: message }))
);
const selectCases = createFeatureSelector<CasesState>('cases');
export const selectViewModel = createSelector(selectCases, state => ({
...state,
visibleItems: state.items.filter(row => state.query.status === 'All' || row.status === state.query.status),
selected: state.items.find(row => row.id === state.selectedId) ?? null
}));
Service boundary and revision checksdemo-api.ts
The local service simulates latency, one-time failures, validation, and stale-write rejection.
import { Injectable } from '@angular/core';
import { Observable, timer, map } from 'rxjs';
import { FIXTURES } from './data';
import { CaseUpdate, Query, SupplierCase } from './models';
@Injectable({ providedIn: 'root' })
export class DemoCasesApi {
private rows = FIXTURES.map(row => ({ ...row }));
failNextLoad = false;
failNextSave = false;
search(query: Query): Observable<readonly SupplierCase[]> {
return timer(450).pipe(map(() => {
if (this.failNextLoad) { this.failNextLoad = false; throw new Error('The queue could not be loaded. Retry with your filters intact.'); }
const term = query.term.trim().toLowerCase();
return this.rows.filter(row => (!term || `${row.id} ${row.supplier} ${row.summary}`.toLowerCase().includes(term)) && (query.status === 'All' || row.status === query.status)).map(row => ({ ...row }));
}));
}
update(update: CaseUpdate): Observable<SupplierCase> {
return timer(600).pipe(map(() => {
if (this.failNextSave) { this.failNextSave = false; throw new Error('The update could not be saved. Your edits are still here; retry when ready.'); }
const index = this.rows.findIndex(row => row.id === update.id);
if (index < 0) throw new Error('The selected case no longer exists.');
if (this.rows[index].revision !== update.revision) throw new Error('This record changed. Reopen it before submitting a new update.');
if (update.owner.trim().length < 3 || update.note.trim().length < 12) throw new Error('Enter an owner and a clear action note.');
const item = { ...this.rows[index], ...update, owner: update.owner.trim(), note: update.note.trim(), revision: update.revision + 1 };
this.rows = this.rows.map((row, position) => position === index ? item : row);
return { ...item };
}));
}
}
