feat(entity): add undefined to Dictionary's index signature

modules/entity/spec/BUILD

@@ -9,6 +9,7 @@ ts_test_library(
     ),
     deps = [
         "//modules/entity",
+        "//modules/store",
         "@npm//rxjs",
     ],
 )
@@ -17,6 +18,5 @@ jasmine_node_test(
     name = "test",
     deps = [
         ":test_lib",
-        "//modules/entity",
     ],
 )

modules/entity/spec/state_selectors.spec.ts

@@ -6,6 +6,7 @@ import {
   AnimalFarm,
   TheGreatGatsby,
 } from './fixtures/book';
+import { MemoizedSelector, createSelector } from '@ngrx/store';
 
 describe('Entity State Selectors', () => {
   describe('Composed Selectors', () => {
@@ -89,6 +90,14 @@ describe('Entity State Selectors', () => {
       expect(entities).toEqual(state.entities);
     });
 
+    it('should type single entity from Dictonary as entity type or undefined', () => {
+      // MemoizedSelector acts like a type checker
+      const singleEnitity: MemoizedSelector<
+        EntityState<BookModel>,
+        BookModel | undefined
+      > = createSelector(selectors.selectEntities, enitites => enitites[0]);
+    });
+
     it('should create a selector for selecting the list of models', () => {
       const models = selectors.selectAll(state);
 

modules/entity/src/models.ts

@@ -9,11 +9,11 @@ export type IdSelectorNum<T> = (model: T) => number;
 export type IdSelector<T> = IdSelectorStr<T> | IdSelectorNum<T>;
 
 export interface DictionaryNum<T> {
-  [id: number]: T;
+  [id: number]: T | undefined;
 }
 
 export abstract class Dictionary<T> implements DictionaryNum<T> {
-  [id: string]: T;
+  [id: string]: T | undefined;
 }
 
 export interface UpdateStr<T> {