NgRx SignalStore Patterns

Quick Guide: Use NgRx SignalStore for reactive client state in Angular 17+. Compose stores with withState, withComputed, withMethods. Use patchState for immutable updates. Use withEntities for collections. NEVER use traditional NgRx patterns (actions, reducers, effects) in new SignalStore code.

Detailed Resources:

• examples/core.md - signalStore, withState, withComputed, withMethods, withProps
• examples/entities.md - withEntities, CRUD operations, prependEntity/upsertEntity (v20+)
• examples/effects.md - rxMethod, signalMethod (v19+), side effects
• examples/features.md - signalStoreFeature, custom features, DevTools
• examples/testing.md - Unit tests, unprotected(), mocking strategies
• examples/migration.md - Migration from traditional NgRx
• reference.md - Decision frameworks, anti-patterns, red flags

---

<critical_requirements>

CRITICAL: Before Managing State with NgRx SignalStore

(You MUST use patchState() for ALL state updates - NEVER mutate state directly)

(You MUST wrap async operations in rxMethod() from @ngrx/signals/rxjs-interop for RxJS integration)

(You MUST use withEntities() from @ngrx/signals/entities for entity collections - NOT arrays in state)

(You MUST use named exports ONLY - NO default exports in any store files)

(You MUST use named constants for ALL numbers - NO magic numbers in state code)

</critical_requirements>

---

Auto-detection: NgRx SignalStore, signalStore, withState, withComputed, withMethods, patchState, withEntities, rxMethod, signalStoreFeature, @ngrx/signals

When to use:

• Managing reactive client state in Angular 17+ applications
• Building composable, reusable store features
• Handling entity collections with CRUD operations
• Integrating RxJS operators for side effects
• Applications requiring fine-grained reactivity with Angular Signals

Key patterns covered:

• Store creation with signalStore() and providedIn options
• State, computed, and methods composition
• Entity management with withEntities
• RxJS integration with rxMethod and signal-only signalMethod
• Custom features with signalStoreFeature and context-aware withFeature (v20+)
• Derived reactive state with withLinkedState (v20+)
• Call state patterns (loading, loaded, error)

When NOT to use:

• Server/API data as primary source (use HTTP services with rxMethod for caching)
• Simple component-local state (use Angular signals directly)
• Projects still on Angular < 17 (requires signals)
• Teams unfamiliar with functional composition patterns

---

Philosophy

NgRx SignalStore is a lightweight, functional state management solution built on Angular Signals. It replaces traditional NgRx patterns (actions, reducers, effects, selectors) with a composable, feature-based approach that eliminates boilerplate while maintaining predictability.

Core Principles:

1. Functional Composition - Build stores by composing features like withState, withComputed, withMethods
2. Signal-Based Reactivity - Leverage Angular's fine-grained reactivity for optimal performance
3. Immutable Updates - Use patchState() for predictable state transitions
4. Extensibility - Create custom features with signalStoreFeature() for reuse across stores

Key Architecture Decisions:

1. signalStore() creates a fully typed store as an injectable Angular service
2. patchState() ensures immutable updates without Immer dependency
3. withEntities() provides standardized entity management (normalized ids/entityMap structure with built-in CRUD updaters)
4. rxMethod() bridges Angular Signals with RxJS for complex async flows
5. Protected state (v18+) prevents external mutations by default; v19+ applies deep freeze recursively

State Ownership:

State Type	Solution	Reason
Server/API data	HTTP services + rxMethod	Caching in store, fetch via services
Shared client state	SignalStore	Reactivity, composition, DevTools
Component-local state	Angular signals	Simpler, no overhead
URL state (filters)	Router query params	Shareable, bookmarkable

---

Core Patterns

Pattern 1: Basic Store with signalStore

Create stores using signalStore() with withState, withComputed, and withMethods.

Feature Ordering

Features execute in order. State features must come first:

1. withState() - Define state
2. withComputed() - Derived values from state
3. withMethods() - Actions that update state
4. withHooks() - Lifecycle hooks (onInit, onDestroy)

For implementation examples, see examples/core.md.

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Pattern 2: State Updates with patchState

Use patchState() for all state modifications. It ensures immutability and proper signal notifications.

When to Use

• Synchronous state updates
• Partial state updates (spread not needed)
• Inside withMethods() and custom features

Key Behaviors

• Accepts partial state object or updater functions
• Multiple updaters can be passed to single call
• Works with entity updaters from @ngrx/signals/entities

For implementation examples, see examples/core.md.

---

Pattern 3: Entity Management with withEntities

Use withEntities() for collections of items with IDs. Provides standardized CRUD operations and efficient lookups.

When to Use

• Lists of items with unique identifiers
• CRUD operations on collections
• Need for efficient ID-based lookups
• Multiple entity collections in one store

Available Updaters

• setAllEntities() - Replace all entities
• addEntity() / addEntities() - Add new entities
• setEntity() / setEntities() - Upsert entities
• updateEntity() / updateEntities() - Partial updates
• removeEntity() / removeEntities() - Delete entities

For implementation examples, see examples/entities.md.

---

Pattern 4: RxJS Integration with rxMethod

Use rxMethod() for side effects that need RxJS operators (debounce, switchMap, etc.).

When to Use

• Debounced search/filtering
• Cancellable HTTP requests
• Complex async flows with multiple operators
• Reactive streams from signals

Key Behaviors

• Accepts Observable<T>, Signal<T>, or T as input
• Factory function receives Observable<T> for piping
• Runs in injection context (can use inject())
• Auto-unsubscribes on store destroy

For implementation examples, see examples/effects.md.

---

Pattern 4b: Signal-Only Side Effects with signalMethod (v19+)

Use signalMethod() for side effects that don't need RxJS operators.

When to Use

• Simple side effects without RxJS dependency
• When you want to work purely with Signals
• Side effects that don't require debounce/switchMap/cancellation
• When injection context is not available

Key Behaviors

• Accepts Signal<T> or T as input (no Observable)
• Processor function runs independently of injection context
• Only parameter signals are tracked; internal signals remain untracked
• You must handle race conditions manually (no built-in switchMap)

rxMethod vs signalMethod

Feature	rxMethod	signalMethod
RxJS required	Yes	No
Operators (debounce, switchMap)	Yes	No
Race condition handling	Built-in	Manual
Input types	T, Signal, Observable	T, Signal

For implementation examples, see examples/effects.md.

---

Pattern 5: Custom Features with signalStoreFeature

Use signalStoreFeature() to create reusable store functionality.

When to Use

• Shared patterns across multiple stores (loading state, error handling)
• Encapsulated feature modules
• Third-party store extensions
• DRY principle for repeated store logic

Type Constraints

Use type() helper to specify required store members:

• Ensures feature is only used with compatible stores
• Provides full type inference
• Enables composition of features

For implementation examples, see examples/features.md.

---

Pattern 6: Lifecycle Hooks with withHooks

Use withHooks() for initialization and cleanup logic.

Available Hooks

• onInit() - Called when store is instantiated
• onDestroy() - Called when store is destroyed

Common Use Cases

• Loading initial data on store creation
• Setting up subscriptions
• Cleanup of resources
• DevTools initialization

For implementation examples, see examples/core.md.

---

Pattern 7: Call State Pattern

Track loading, loaded, and error states for async operations using withCallState() from ngrx-toolkit or custom implementation.

States

• loading - Operation in progress
• loaded - Operation completed successfully
• error - Operation failed with error

Benefits

• Consistent loading UI patterns
• Error handling standardization
• Multiple collection support
• DevTools visibility

For implementation examples, see examples/features.md.

---

Pattern 8: Context-Aware Features with withFeature (v20+)

Use withFeature() to create features that have access to the current store's methods and properties. Unlike signalStoreFeature(), withFeature receives the store instance, enabling reusable features that can call store-specific methods.

When to Use

• Features that need to call existing store methods
• Generic patterns like entity loaders that need store-specific fetch logic
• When signalStoreFeature() is insufficient because the feature needs store context

import { withFeature } from "@ngrx/signals";

// withFeature receives the store instance
export const ProductStore = signalStore(
  { providedIn: "root" },
  withMethods((store) => ({
    load: rxMethod<string>(/* fetch logic */),
  })),
  withFeature((store) =>
    withEntityLoader((id) => firstValueFrom(store.load(id))),
  ),
);

---

Pattern 9: Derived Reactive State with withLinkedState (v20+)

Use withLinkedState() to create state signals that are automatically recomputed when their source signals change. Unlike withComputed(), linked state is writable and can be overridden.

When to Use

• Derived state that also needs to be independently settable
• Maintaining selection state across data changes
• State that has a default derived value but can be overridden by user action

import { withLinkedState } from "@ngrx/signals";

export const FilterStore = signalStore(
  withState({ items: [] as Item[] }),
  withLinkedState(({ items }) => ({
    // Recomputes when items change, but can also be set independently
    selectedId: () => items()[0]?.id ?? null,
  })),
);

---

Integration Guide

Angular DI Integration:

SignalStore is an Angular service. Use { providedIn: 'root' } for singletons or component-level providers: [Store] for scoped instances that are destroyed with the component.

See examples/core.md Pattern 5 and Component-Level Stores for DI patterns.

DevTools Integration:

Use withDevtools('name') from @angular-architects/ngrx-toolkit for Redux DevTools support. Place it before withState in the feature chain.

See examples/features.md Pattern 5 for setup.

Testing Integration:

• Use unprotected() from @ngrx/signals/testing to bypass state protection for test setup
• Use TestBed.configureTestingModule() with mocked services
• Test store methods directly or through component integration

See examples/testing.md for patterns.

---

<red_flags>

RED FLAGS

High Priority Issues:

• Mutating state directly instead of using patchState - breaks reactivity and signal notifications
• Using arrays instead of withEntities for entity collections - loses normalized state, O(1) lookups
• Not wrapping async RxJS flows in rxMethod - loses cancellation and proper cleanup
• Accessing store state outside computed/template - may not trigger updates

Medium Priority Issues:

• Missing error handling in rxMethod pipelines
• Deeply nested state (flatten with multiple state slices)
• Not using entityConfig() for custom entity IDs (v18+)
• Using signalMethod for async operations with race conditions (use rxMethod with switchMap)

Gotchas & Edge Cases:

• withHooks.onInit() runs during store instantiation - be careful with side effects in tests
• patchState with entity updaters requires collection option when using named collections
• rxMethod auto-unsubscribes on destroy - do not manually unsubscribe
• Protected state (v18+) prevents external patchState calls by default
• Feature execution order matters - later features can access earlier ones
• v19+ Deep Freeze: State values are recursively frozen with Object.freeze in dev mode - use withProps() for mutable objects like FormGroup

See reference.md for detailed anti-patterns with code examples.

</red_flags>

---

<critical_reminders>

CRITICAL REMINDERS

(You MUST use patchState() for ALL state updates - NEVER mutate state directly)

(You MUST wrap async operations in rxMethod() from @ngrx/signals/rxjs-interop for RxJS integration)

(You MUST use withEntities() from @ngrx/signals/entities for entity collections - NOT arrays in state)

(You MUST use named exports ONLY - NO default exports in any store files)

(You MUST use named constants for ALL numbers - NO magic numbers in state code)

Failure to follow these rules will cause reactivity bugs, state corruption, and inconsistent behavior.

</critical_reminders>