diff --git a/src/lib/services/entities-map.service.ts b/src/lib/services/entities-map.service.ts
new file mode 100644
index 0000000..031e557
--- /dev/null
+++ b/src/lib/services/entities-map.service.ts
@@ -0,0 +1,108 @@
+import { Inject, Injectable } from '@angular/core';
+import { BehaviorSubject, Observable, Subject } from 'rxjs';
+import { filter, startWith } from 'rxjs/operators';
+import { Entity } from '../listing';
+import { RequiredParam, shareLast, Validate } from '../utils';
+
+@Injectable({ providedIn: 'root' })
+export abstract class EntitiesMapService<E extends Entity<I>, I> {
+    protected readonly _map = new Map<string, BehaviorSubject<E[]>>();
+    private readonly _entityChanged$ = new Subject<E>();
+    private readonly _entityDeleted$ = new Subject<E>();
+
+    protected constructor(@Inject('ENTITY_PRIMARY_KEY') protected readonly _primaryKey: string) {}
+
+    get$(key: string) {
+        if (!this._map.has(key)) {
+            this._map.set(key, new BehaviorSubject<E[]>([]));
+        }
+
+        return this._getBehaviourSubject(key).asObservable();
+    }
+
+    has(dossierId: string) {
+        return this._map.has(dossierId);
+    }
+
+    get(key: string): E[];
+    get(key: string, id: string): E | undefined;
+    get(key: string, id?: string): E | E[] | undefined {
+        const value = this._getBehaviourSubject(key)?.value;
+        if (!id) {
+            return value ?? [];
+        }
+        return value?.find(item => item.id === id);
+    }
+
+    set(key: string, entities: E[]): void {
+        if (!this._map.has(key)) {
+            this._map.set(key, new BehaviorSubject<E[]>(entities));
+            return entities.forEach(entity => this._entityChanged$.next(entity));
+        }
+
+        const changedEntities: E[] = [];
+        const deletedEntities = this.get(key).filter(oldEntity => !entities.find(newEntity => newEntity.id === oldEntity.id));
+
+        // Keep old object references for unchanged entities
+        const newEntities: E[] = entities.map(newEntity => {
+            const oldEntity: E | undefined = this.get(key, newEntity.id);
+
+            if (oldEntity && newEntity.isEqual(oldEntity)) {
+                return oldEntity;
+            }
+
+            changedEntities.push(newEntity);
+            return newEntity;
+        });
+
+        this._getBehaviourSubject(key).next(newEntities);
+
+        // Emit observables only after entities have been updated
+
+        for (const entity of changedEntities) {
+            this._entityChanged$.next(entity);
+        }
+
+        for (const entity of deletedEntities) {
+            this._entityDeleted$.next(entity);
+        }
+    }
+
+    replace(entities: E[]) {
+        const key = this._pluckPrimaryKey(entities[0]);
+        const entityIds = entities.map(entity => entity.id);
+        const existingEntities = this.get(key).filter(entity => entityIds.includes(entity.id));
+        const newEntities = entities.filter(entity => {
+            const old = existingEntities.find(e => e.id === entity.id);
+            return !old || !entity.isEqual(old);
+        });
+        if (newEntities.length) {
+            const all = this.get(key).filter(e => !newEntities.map(entity => entity.id).includes(e.id));
+            this.set(key, [...all, ...newEntities]);
+        }
+    }
+
+    @Validate()
+    watch$(@RequiredParam() key: string, @RequiredParam() entityId: string): Observable<E> {
+        return this._entityChanged$.pipe(
+            filter(entity => entity.id === entityId),
+            startWith(this.get(key, entityId) as E),
+            shareLast(),
+        );
+    }
+
+    watchDeleted$(entityId: string): Observable<E> {
+        return this._entityDeleted$.pipe(filter(entity => entity.id === entityId));
+    }
+
+    private _pluckPrimaryKey(entity: E): string {
+        // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+        // @ts-ignore
+        return entity[this._primaryKey] as string;
+    }
+
+    private _getBehaviourSubject(key: string): BehaviorSubject<E[]> {
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        return this._map.get(key)!;
+    }
+}
diff --git a/src/lib/services/index.ts b/src/lib/services/index.ts
index 026ff9d..365ad26 100644
--- a/src/lib/services/index.ts
+++ b/src/lib/services/index.ts
@@ -4,3 +4,4 @@ export * from './error-message.service';
 export * from './generic.service';
 export * from './composite-route.guard';
 export * from './stats.service';
+export * from './entities-map.service';