diff --git a/libs/ngrx-toolkit/src/lib/with-data-service.spec.ts b/libs/ngrx-toolkit/src/lib/with-data-service.spec.ts
index 075e064..3abcf2c 100644
--- a/libs/ngrx-toolkit/src/lib/with-data-service.spec.ts
+++ b/libs/ngrx-toolkit/src/lib/with-data-service.spec.ts
@@ -1,9 +1,8 @@
 import { Injectable } from '@angular/core';
 import { fakeAsync, TestBed, tick } from '@angular/core/testing';
-import { Observable, firstValueFrom, of, delay } from 'rxjs';
 import { signalStore, type } from '@ngrx/signals';
-import { withEntities } from '@ngrx/signals/entities';
-import { EntityId } from '@ngrx/signals/entities';
+import { EntityId, withEntities } from '@ngrx/signals/entities';
+import { delay, firstValueFrom, Observable, of } from 'rxjs';
 import { withCallState } from './with-call-state';
 import { DataService, withDataService } from './with-data-service';
 
@@ -39,6 +38,19 @@ describe('withDataService', () => {
       expect(store.flightEntities().length).toBe(1);
     });
   }));
+  it('should load from a service and set entities in the store (with named selectId)', fakeAsync(() => {
+    TestBed.runInInjectionContext(() => {
+      const store = new StoreWithSelectId();
+
+      tick();
+      expect(store.entities().length).toBe(0);
+
+      store.load();
+      tick();
+
+      expect(store.entities().length).toBe(1);
+    });
+  }));
   it('should load by ID from a service and set entities in the store', fakeAsync(() => {
     TestBed.runInInjectionContext(() => {
       const store = new Store();
@@ -65,6 +77,21 @@ describe('withDataService', () => {
       expect(store.currentFlight()).toEqual(createFlight({ id: 2 }));
     });
   }));
+  it('should load by ID from a service and set entities in the store (with named selectId)', fakeAsync(() => {
+    TestBed.runInInjectionContext(() => {
+      const store = new StoreWithSelectId();
+
+      tick();
+
+      store.loadById(2);
+
+      tick();
+
+      expect(store.current()).toEqual(
+        createFlightWithCustomId({ flightId: '2' })
+      );
+    });
+  }));
   it('should create from a service and set an entity in the store', fakeAsync(() => {
     TestBed.runInInjectionContext(() => {
       const store = new Store();
@@ -97,6 +124,24 @@ describe('withDataService', () => {
       expect(store.currentFlight()).toEqual(createFlight({ id: 3 }));
     });
   }));
+  it('should create from a service and set an entity in the store (with named selectId)', fakeAsync(() => {
+    TestBed.runInInjectionContext(() => {
+      const store = new StoreWithSelectId();
+
+      tick();
+
+      expect(store.entities().length).toBe(0);
+
+      store.create(createFlightWithCustomId({ flightId: '3' }));
+
+      tick();
+
+      expect(store.entities().length).toBe(1);
+      expect(store.current()).toEqual(
+        createFlightWithCustomId({ flightId: '3' })
+      );
+    });
+  }));
   it('should update from a service and update an entity in the store', fakeAsync(() => {
     TestBed.runInInjectionContext(() => {
       const store = new Store();
@@ -129,6 +174,26 @@ describe('withDataService', () => {
       expect(store.currentFlight()).toEqual(createFlight({ id: 3 }));
     });
   }));
+  it('should update from a service and update an entity in the store (with named selectId)', fakeAsync(() => {
+    TestBed.runInInjectionContext(() => {
+      const store = new StoreWithSelectId();
+
+      tick();
+
+      expect(store.entities().length).toBe(0);
+
+      store.create(
+        createFlightWithCustomId({ flightId: '3', from: 'Wadena MN' })
+      );
+      tick();
+      store.update(createFlightWithCustomId({ flightId: '3' }));
+      tick();
+
+      expect(store.current()).toEqual(
+        createFlightWithCustomId({ flightId: '3' })
+      );
+    });
+  }));
   it('should update all from a service and update all entities in the store', fakeAsync(() => {
     TestBed.runInInjectionContext(() => {
       const store = new Store();
@@ -165,6 +230,35 @@ describe('withDataService', () => {
       expect(store.flightEntities().at(1)).toEqual(createFlight({ id: 4 }));
     });
   }));
+  it('should update all from a service and update all entities in the store (with named selectId)', fakeAsync(() => {
+    TestBed.runInInjectionContext(() => {
+      const store = new StoreWithSelectId();
+
+      tick();
+
+      expect(store.entities().length).toBe(0);
+
+      store.create(
+        createFlightWithCustomId({ flightId: '3', from: 'Wadena MN' })
+      );
+      store.create(
+        createFlightWithCustomId({ flightId: '4', from: 'Wadena MN' })
+      );
+      tick();
+      store.updateAll([
+        createFlightWithCustomId({ flightId: '3' }),
+        createFlightWithCustomId({ flightId: '4' }),
+      ]);
+      tick();
+      expect(store.entities().length).toBe(2);
+      expect(store.entities().at(0)).toEqual(
+        createFlightWithCustomId({ flightId: '3' })
+      );
+      expect(store.entities().at(1)).toEqual(
+        createFlightWithCustomId({ flightId: '4' })
+      );
+    });
+  }));
   it('should delete from a service and update that entity in the store', fakeAsync(() => {
     TestBed.runInInjectionContext(() => {
       const store = new Store();
@@ -199,6 +293,25 @@ describe('withDataService', () => {
       expect(store.flightEntities().length).toBe(0);
     });
   }));
+  it('should delete from a service and update that entity in the store (with named selectId)', fakeAsync(() => {
+    TestBed.runInInjectionContext(() => {
+      const store = new StoreWithSelectId();
+
+      tick();
+
+      expect(store.entities().length).toBe(0);
+
+      store.create(createFlightWithCustomId({ flightId: '3' }));
+      tick();
+      expect(store.entities().length).toBe(1);
+      expect(store.entities().at(0)).toEqual(
+        createFlightWithCustomId({ flightId: '3' })
+      );
+      store.delete(createFlightWithCustomId({ flightId: '3' }));
+      tick();
+      expect(store.entities().length).toBe(0);
+    });
+  }));
   it('should update the selected flight of the store', fakeAsync(() => {
     TestBed.runInInjectionContext(() => {
       const store = new Store();
@@ -235,6 +348,25 @@ describe('withDataService', () => {
       );
     });
   }));
+  it('should update selected flight of the store (with named selectId)', fakeAsync(() => {
+    TestBed.runInInjectionContext(() => {
+      const store = new StoreWithSelectId();
+
+      tick();
+
+      store.create(createFlightWithCustomId({ flightId: '3' }));
+      expect(store.selectedEntities().length).toBe(0);
+
+      store.updateSelected('3', true);
+
+      tick();
+
+      expect(store.selectedEntities().length).toBe(1);
+      expect(store.selectedEntities()).toContainEqual(
+        createFlightWithCustomId({ flightId: '3' })
+      );
+    });
+  }));
   it('should update the filter of the service', fakeAsync(() => {
     TestBed.runInInjectionContext(() => {
       const store = new Store();
@@ -268,6 +400,21 @@ describe('withDataService', () => {
       });
     });
   }));
+  it('should update the filter of the service (with named selectId)', fakeAsync(() => {
+    TestBed.runInInjectionContext(() => {
+      const store = new StoreWithSelectId();
+
+      tick();
+
+      expect(store.filter()).toEqual({ from: 'Paris', to: 'New York' });
+
+      store.updateFilter({ from: 'Wadena MN', to: 'New York' });
+
+      tick();
+
+      expect(store.filter()).toEqual({ from: 'Wadena MN', to: 'New York' });
+    });
+  }));
   it('should set the current entity', fakeAsync(() => {
     TestBed.runInInjectionContext(() => {
       const store = new Store();
@@ -292,6 +439,20 @@ describe('withDataService', () => {
       expect(store.currentFlight()).toEqual(createFlight({ id: 4 }));
     });
   }));
+  it('should set the current entity (with named selectId)', fakeAsync(() => {
+    TestBed.runInInjectionContext(() => {
+      const store = new StoreWithSelectId();
+      tick();
+
+      store.create(createFlightWithCustomId({ flightId: '3' }));
+
+      store.setCurrent(createFlightWithCustomId({ flightId: '4' }));
+
+      expect(store.current()).toEqual(
+        createFlightWithCustomId({ flightId: '4' })
+      );
+    });
+  }));
 
   it('handles loading state', fakeAsync(() => {
     TestBed.runInInjectionContext(() => {
@@ -415,6 +576,19 @@ const createFlight = (flight: Partial<Flight> = {}) => ({
   },
   ...flight,
 });
+
+let currentCustomFlightId = 0;
+const createFlightWithCustomId = (
+  flight: Partial<FlightWithCustomId> = {}
+): FlightWithCustomId => ({
+  flightId: `${++currentCustomFlightId}`,
+  from: 'Paris',
+  to: 'New York',
+  date: new Date().toDateString(),
+  delayed: false,
+  ...flight,
+});
+
 type Flight = {
   id: number;
   from: string;
@@ -423,6 +597,8 @@ type Flight = {
   delayed: boolean;
 };
 
+type FlightWithCustomId = Omit<Flight, 'id'> & { flightId: string };
+
 type FlightFilter = {
   from: string;
   to: string;
@@ -473,6 +649,53 @@ class MockFlightService implements DataService<Flight, FlightFilter> {
   }
 }
 
+@Injectable({
+  providedIn: 'root',
+})
+class MockFlightWithSelectIdService
+  implements DataService<FlightWithCustomId, FlightFilter>
+{
+  loadById(id: EntityId): Promise<FlightWithCustomId> {
+    return firstValueFrom(this.findById('' + id));
+  }
+
+  create(entity: FlightWithCustomId): Promise<FlightWithCustomId> {
+    return firstValueFrom(this.save(entity));
+  }
+
+  update(entity: FlightWithCustomId): Promise<FlightWithCustomId> {
+    return firstValueFrom(this.save(entity));
+  }
+
+  updateAll(entity: FlightWithCustomId[]): Promise<FlightWithCustomId[]> {
+    return firstValueFrom(of(entity));
+  }
+
+  delete(entity: FlightWithCustomId): Promise<void> {
+    return firstValueFrom(this.remove(entity));
+  }
+
+  load(filter: FlightFilter): Promise<FlightWithCustomId[]> {
+    return firstValueFrom(this.find(filter.from, filter.to));
+  }
+
+  private find(_from: string, _to: string): Observable<FlightWithCustomId[]> {
+    return of([createFlightWithCustomId()]);
+  }
+
+  private findById(id: string): Observable<FlightWithCustomId> {
+    return of(createFlightWithCustomId({ flightId: id }));
+  }
+
+  private save(flight: FlightWithCustomId): Observable<FlightWithCustomId> {
+    return of(flight);
+  }
+
+  private remove(_flight: FlightWithCustomId): Observable<void> {
+    return of(undefined);
+  }
+}
+
 @Injectable({
   providedIn: 'root',
 })
@@ -563,3 +786,15 @@ const StoreWithNamedCollectionForLoading = signalStore(
     collection: 'flight',
   })
 );
+
+const StoreWithSelectId = signalStore(
+  withCallState(),
+  withEntities({
+    entity: type<FlightWithCustomId>(),
+  }),
+  withDataService({
+    dataServiceType: MockFlightWithSelectIdService,
+    filter: { from: 'Paris', to: 'New York' },
+    selectId: (flight: FlightWithCustomId) => flight.flightId,
+  })
+);
diff --git a/libs/ngrx-toolkit/src/lib/with-data-service.ts b/libs/ngrx-toolkit/src/lib/with-data-service.ts
index b63185a..6b4816b 100644
--- a/libs/ngrx-toolkit/src/lib/with-data-service.ts
+++ b/libs/ngrx-toolkit/src/lib/with-data-service.ts
@@ -1,14 +1,24 @@
 import { ProviderToken, Signal, computed, inject } from '@angular/core';
 import {
+  EmptyFeatureResult,
   SignalStoreFeature,
+  WritableStateSource,
   patchState,
   signalStoreFeature,
   withComputed,
   withMethods,
   withState,
-  EmptyFeatureResult,
-  WritableStateSource,
 } from '@ngrx/signals';
+import {
+  EntityId,
+  NamedEntityState,
+  SelectEntityId,
+  addEntity,
+  removeEntity,
+  setAllEntities,
+  updateEntity,
+} from '@ngrx/signals/entities';
+import { EntityState } from './shared/signal-store-models';
 import {
   CallState,
   NamedCallStateSlice,
@@ -17,18 +27,9 @@ import {
   setLoaded,
   setLoading,
 } from './with-call-state';
-import {
-  NamedEntityState,
-  setAllEntities,
-  EntityId,
-  addEntity,
-  updateEntity,
-  removeEntity,
-} from '@ngrx/signals/entities';
-import { EntityState } from './shared/signal-store-models';
 
 export type Filter = Record<string, unknown>;
-export type Entity = { id: EntityId };
+export type Entity = Record<string, unknown>;
 
 export interface DataService<E extends Entity, F extends Filter> {
   load(filter: F): Promise<E[]>;
@@ -121,6 +122,16 @@ export function getDataServiceKeys(options: { collection?: string }) {
   };
 }
 
+const selectEntityId = <E extends Entity>(
+  selectId?: SelectEntityId<E>
+): SelectEntityId<E> => {
+  if (typeof selectId === 'function') {
+    return selectId;
+  }
+
+  return (entity: E) => entity['id'] as EntityId;
+};
+
 export type NamedDataServiceState<
   E extends Entity,
   F extends Filter,
@@ -202,6 +213,7 @@ export function withDataService<
   dataServiceType: ProviderToken<DataService<E, F>>;
   filter: F;
   collection: Collection;
+  selectId?: SelectEntityId<E>;
 }): SignalStoreFeature<
   EmptyFeatureResult & {
     state: NamedCallStateSlice<Collection> & NamedEntityState<E, Collection>;
@@ -215,6 +227,7 @@ export function withDataService<
 export function withDataService<E extends Entity, F extends Filter>(options: {
   dataServiceType: ProviderToken<DataService<E, F>>;
   filter: F;
+  selectId?: SelectEntityId<E>;
 }): SignalStoreFeature<
   EmptyFeatureResult & { state: { callState: CallState } & EntityState<E> },
   {
@@ -232,6 +245,7 @@ export function withDataService<
   dataServiceType: ProviderToken<DataService<E, F>>;
   filter: F;
   collection?: Collection;
+  selectId?: SelectEntityId<E>;
 }): /* eslint-disable @typescript-eslint/no-explicit-any */
 SignalStoreFeature<any, any> {
   const { dataServiceType, filter, collection: prefix } = options;
@@ -243,7 +257,6 @@ SignalStoreFeature<any, any> {
     selectedIdsKey,
     updateFilterKey,
     updateSelectedKey,
-
     currentKey,
     createKey,
     updateKey,
@@ -253,6 +266,8 @@ SignalStoreFeature<any, any> {
     setCurrentKey,
   } = getDataServiceKeys(options);
 
+  const selectId = selectEntityId(options.selectId);
+
   const { callStateKey } = getCallStateKeys({ collection: prefix });
 
   return signalStoreFeature(
@@ -269,7 +284,7 @@ SignalStoreFeature<any, any> {
 
       return {
         [selectedEntitiesKey]: computed(() =>
-          entities().filter((e) => selectedIds()[e.id])
+          entities().filter((e) => selectedIds()[selectId(e)])
         ),
       };
     }),
@@ -298,8 +313,8 @@ SignalStoreFeature<any, any> {
               patchState(
                 store,
                 prefix
-                  ? setAllEntities(result, { collection: prefix })
-                  : setAllEntities(result)
+                  ? setAllEntities(result, { collection: prefix, selectId })
+                  : setAllEntities(result, { selectId })
               );
               (() =>
                 store[callStateKey] && patchState(store, setLoaded(prefix)))();
@@ -340,8 +355,8 @@ SignalStoreFeature<any, any> {
               patchState(
                 store,
                 prefix
-                  ? addEntity(created, { collection: prefix })
-                  : addEntity(created)
+                  ? addEntity(created, { collection: prefix, selectId })
+                  : addEntity(created, { selectId })
               );
               (() =>
                 store[callStateKey] && patchState(store, setLoaded(prefix)))();
@@ -362,12 +377,12 @@ SignalStoreFeature<any, any> {
               patchState(store, { [currentKey]: updated });
 
               const updateArg = {
-                id: updated.id,
+                id: selectId(entity),
                 changes: updated,
               };
 
               const updater = (collection: string) =>
-                updateEntity(updateArg, { collection });
+                updateEntity(updateArg, { collection, selectId });
 
               patchState(
                 store,
@@ -391,8 +406,8 @@ SignalStoreFeature<any, any> {
               patchState(
                 store,
                 prefix
-                  ? setAllEntities(result, { collection: prefix })
-                  : setAllEntities(result)
+                  ? setAllEntities(result, { collection: prefix, selectId })
+                  : setAllEntities(result, { selectId })
               );
               (() =>
                 store[callStateKey] && patchState(store, setLoaded(prefix)))();
@@ -409,13 +424,15 @@ SignalStoreFeature<any, any> {
               store[callStateKey] && patchState(store, setLoading(prefix)))();
 
             try {
+              const id = selectId(entity);
+
               await dataService.delete(entity);
               patchState(store, { [currentKey]: undefined });
               patchState(
                 store,
                 prefix
-                  ? removeEntity(entity.id, { collection: prefix })
-                  : removeEntity(entity.id)
+                  ? removeEntity(id, { collection: prefix })
+                  : removeEntity(id)
               );
               (() =>
                 store[callStateKey] && patchState(store, setLoaded(prefix)))();