diff --git a/src/lib/listing/models/entity.model.ts b/src/lib/listing/models/entity.model.ts
index b8fc65f..fb4d63a 100644
--- a/src/lib/listing/models/entity.model.ts
+++ b/src/lib/listing/models/entity.model.ts
@@ -1,7 +1,8 @@
 import { IListable } from './listable';
+import { Id } from './trackable';
 
 export abstract class Entity<I> implements IListable {
-    abstract readonly id: string;
+    abstract readonly id: Id;
     abstract readonly routerLink?: string;
     abstract readonly searchKey: string;
 
diff --git a/src/lib/listing/models/trackable.ts b/src/lib/listing/models/trackable.ts
index b752b41..66c3fb4 100644
--- a/src/lib/listing/models/trackable.ts
+++ b/src/lib/listing/models/trackable.ts
@@ -1,3 +1,5 @@
+export type Id = string | number;
+
 export interface ITrackable {
-    readonly id: string;
+    readonly id: Id;
 }
diff --git a/src/lib/listing/services/entities.service.ts b/src/lib/listing/services/entities.service.ts
index 218d49d..ab843a6 100644
--- a/src/lib/listing/services/entities.service.ts
+++ b/src/lib/listing/services/entities.service.ts
@@ -4,6 +4,7 @@ import { filter, map, startWith, tap } from 'rxjs/operators';
 import { IListable } from '../models';
 import { GenericService, QueryParam } from '../../services';
 import { getLength, List, mapEach, shareDistinctLast, shareLast } from '../../utils';
+import { Id } from '../models/trackable';
 
 @Injectable()
 /**
@@ -47,7 +48,7 @@ export class EntitiesService<I, E extends I & IListable = I & IListable> extends
         );
     }
 
-    getEntityChanged$(entityId: string): Observable<E | undefined> {
+    getEntityChanged$(entityId: Id): Observable<E | undefined> {
         return this._entityChanged$.pipe(
             filter(entity => entity.id === entityId),
             startWith(this.find(entityId)),
@@ -55,7 +56,7 @@ export class EntitiesService<I, E extends I & IListable = I & IListable> extends
         );
     }
 
-    getEntityDeleted$(entityId: string): Observable<E | undefined> {
+    getEntityDeleted$(entityId: Id): Observable<E | undefined> {
         return this._entityDeleted$.pipe(filter(entity => entity.id === entityId));
     }
 
@@ -88,7 +89,7 @@ export class EntitiesService<I, E extends I & IListable = I & IListable> extends
         }
     }
 
-    remove(id: string) {
+    remove(id: Id) {
         const entity = this.all.find(item => item.id === id);
         if (entity) {
             this.#all$.next(this.all.filter(item => item.id !== id));
@@ -96,11 +97,11 @@ export class EntitiesService<I, E extends I & IListable = I & IListable> extends
         }
     }
 
-    find(id: string): E | undefined {
+    find(id: Id): E | undefined {
         return this.all.find(entity => entity.id === id);
     }
 
-    has(id: string): boolean {
+    has(id: Id): boolean {
         return this.all.some(entity => entity.id === id);
     }
 
diff --git a/src/lib/services/entities-map.service.ts b/src/lib/services/entities-map.service.ts
index 220d47f..4642c15 100644
--- a/src/lib/services/entities-map.service.ts
+++ b/src/lib/services/entities-map.service.ts
@@ -3,12 +3,13 @@ import { BehaviorSubject, Observable, Subject } from 'rxjs';
 import { filter, startWith } from 'rxjs/operators';
 import { Entity } from '../listing';
 import { RequiredParam, shareLast, Validate } from '../utils';
+import { Id } from '../listing/models/trackable';
 
 @Injectable({ providedIn: 'root' })
 export abstract class EntitiesMapService<E extends Entity<I>, I> {
     protected abstract readonly _primaryKey: string;
 
-    protected readonly _map = new Map<string, BehaviorSubject<E[]>>();
+    protected readonly _map = new Map<Id, BehaviorSubject<E[]>>();
     readonly #entityChanged$ = new Subject<E>();
     readonly #entityDeleted$ = new Subject<E>();
 
@@ -16,11 +17,11 @@ export abstract class EntitiesMapService<E extends Entity<I>, I> {
         return this._map.size === 0;
     }
 
-    delete(keys: string[]): void {
+    delete(keys: Id[]): void {
         keys.forEach(key => this._map.delete(key));
     }
 
-    get$(key: string) {
+    get$(key: Id) {
         if (!this._map.has(key)) {
             this._map.set(key, new BehaviorSubject<E[]>([]));
         }
@@ -28,13 +29,13 @@ export abstract class EntitiesMapService<E extends Entity<I>, I> {
         return this._getBehaviourSubject(key).asObservable();
     }
 
-    has(parentId: string) {
+    has(parentId: Id) {
         return this._map.has(parentId);
     }
 
-    get(key: string): E[];
-    get(key: string, id: string): E | undefined;
-    get(key: string, id?: string): E | E[] | undefined {
+    get(key: Id): E[];
+    get(key: Id, id: Id): E | undefined;
+    get(key: Id, id?: Id): E | E[] | undefined {
         const value = this._getBehaviourSubject(key)?.value;
         if (!id) {
             return value ?? [];
@@ -42,7 +43,7 @@ export abstract class EntitiesMapService<E extends Entity<I>, I> {
         return value?.find(item => item.id === id);
     }
 
-    set(key: string, entities: E[]): void {
+    set(key: Id, entities: E[]): void {
         if (!this._map.has(key)) {
             this._map.set(key, new BehaviorSubject<E[]>(entities));
             return entities.forEach(entity => this.#entityChanged$.next(entity));
@@ -96,7 +97,7 @@ export abstract class EntitiesMapService<E extends Entity<I>, I> {
     }
 
     @Validate()
-    watch$(@RequiredParam() key: string, @RequiredParam() entityId: string): Observable<E> {
+    watch$(@RequiredParam() key: Id, @RequiredParam() entityId: Id): Observable<E> {
         return this.#entityChanged$.pipe(
             filter(entity => entity.id === entityId),
             startWith(this.get(key, entityId) as E),
@@ -104,17 +105,17 @@ export abstract class EntitiesMapService<E extends Entity<I>, I> {
         );
     }
 
-    watchDeleted$(entityId: string): Observable<E> {
+    watchDeleted$(entityId: Id): Observable<E> {
         return this.#entityDeleted$.pipe(filter(entity => entity.id === entityId));
     }
 
-    private _pluckPrimaryKey(entity: E): string {
+    private _pluckPrimaryKey(entity: E): Id {
         // eslint-disable-next-line @typescript-eslint/ban-ts-comment
         // @ts-ignore
-        return entity[this._primaryKey] as string;
+        return entity[this._primaryKey] as Id;
     }
 
-    private _getBehaviourSubject(key: string): BehaviorSubject<E[]> {
+    private _getBehaviourSubject(key: Id): BehaviorSubject<E[]> {
         // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
         return this._map.get(key)!;
     }
diff --git a/src/lib/utils/functions.ts b/src/lib/utils/functions.ts
index f7c5408..510f3ad 100644
--- a/src/lib/utils/functions.ts
+++ b/src/lib/utils/functions.ts
@@ -1,4 +1,4 @@
-import { ITrackable } from '../listing/models/trackable';
+import { Id, ITrackable } from '../listing/models/trackable';
 import { UntypedFormGroup } from '@angular/forms';
 import { forOwn, has, isEqual, isPlainObject, transform } from 'lodash-es';
 import dayjs, { Dayjs } from 'dayjs';
@@ -34,7 +34,7 @@ export function toNumber(str: string): number {
 }
 
 export function trackByFactory<T extends ITrackable>() {
-    return (_index: number, item: T): string => item.id;
+    return (_index: number, item: T): Id => item.id;
 }
 
 export function hasFormChanged(form: UntypedFormGroup, initialFormValue: Record<string, string>): boolean {