diff --git a/libs/ngrx-entity-relationship/e2e/custom-keys-for-entities.spec.ts b/libs/ngrx-entity-relationship/e2e/custom-keys-for-entities.spec.ts
new file mode 100644
index 000000000..69169e457
--- /dev/null
+++ b/libs/ngrx-entity-relationship/e2e/custom-keys-for-entities.spec.ts
@@ -0,0 +1,85 @@
+import {
+    ngrxEntityRelationshipReducer,
+    reduceGraph,
+    relatedEntitySelector,
+    rootEntitySelector,
+    stateKeys,
+} from 'ngrx-entity-relationship';
+
+describe('custom-keys-for-entities', () => {
+    interface Item {
+        id: string;
+        name: string;
+        parentId?: string;
+        parent?: Item;
+    }
+
+    const state: {
+        records: {
+            ids: Array<string>;
+            byId: Record<string, Item | undefined>;
+        };
+    } = {
+        records: {
+            ids: [],
+            byId: {},
+        },
+    };
+
+    const selectItemsState = (s: typeof state) => s.records;
+    const featureSelector = stateKeys(selectItemsState, 'byId');
+
+    const sItem = rootEntitySelector(featureSelector);
+    const sItemParent = relatedEntitySelector(featureSelector, 'parentId', 'parent');
+
+    const selector = sItem(sItemParent());
+
+    it('handles custom values correctly', () => {
+        const action = reduceGraph({
+            data: [
+                {
+                    id: 'i1',
+                    name: '1',
+                    parentId: 'i2',
+                    parent: {
+                        id: 'i2',
+                        name: '2',
+                    },
+                },
+            ],
+            selector,
+        });
+
+        const reducer = ngrxEntityRelationshipReducer<typeof state>(((s: typeof state) => s) as any);
+        const testingState = reducer(state, action);
+
+        // data has been reduced.
+        expect(testingState).toEqual({
+            records: {
+                ids: ['i1', 'i2'],
+                byId: {
+                    i1: {
+                        id: 'i1',
+                        name: '1',
+                        parentId: 'i2',
+                    },
+                    i2: {
+                        id: 'i2',
+                        name: '2',
+                    },
+                },
+            },
+        });
+
+        // data has been reached.
+        expect(selector(testingState, 'i1')).toEqual({
+            id: 'i1',
+            name: '1',
+            parentId: 'i2',
+            parent: {
+                id: 'i2',
+                name: '2',
+            },
+        });
+    });
+});
diff --git a/libs/ngrx-entity-relationship/e2e/custom-keys-no-id.spec.ts b/libs/ngrx-entity-relationship/e2e/custom-keys-no-id.spec.ts
new file mode 100644
index 000000000..550c8abdc
--- /dev/null
+++ b/libs/ngrx-entity-relationship/e2e/custom-keys-no-id.spec.ts
@@ -0,0 +1,82 @@
+import {
+    ngrxEntityRelationshipReducer,
+    reduceGraph,
+    relatedEntitySelector,
+    rootEntitySelector,
+    stateKeys,
+} from 'ngrx-entity-relationship';
+
+describe('custom-keys-no-id', () => {
+    interface Item {
+        id: string;
+        name: string;
+        parentId?: string;
+        parent?: Item;
+    }
+
+    const state: {
+        records: {
+            byId: Record<string, Item | undefined>;
+        };
+    } = {
+        records: {
+            byId: {},
+        },
+    };
+
+    const selectItemsState = (s: typeof state) => s.records;
+    const featureSelector = stateKeys(selectItemsState, 'byId');
+
+    const sItem = rootEntitySelector(featureSelector);
+    const sItemParent = relatedEntitySelector(featureSelector, 'parentId', 'parent');
+
+    const selector = sItem(sItemParent());
+
+    it('handles custom values correctly', () => {
+        const action = reduceGraph({
+            data: [
+                {
+                    id: 'i1',
+                    name: '1',
+                    parentId: 'i2',
+                    parent: {
+                        id: 'i2',
+                        name: '2',
+                    },
+                },
+            ],
+            selector,
+        });
+
+        const reducer = ngrxEntityRelationshipReducer<typeof state>(((s: typeof state) => s) as any);
+        const testingState = reducer(state, action);
+
+        // data has been reduced.
+        expect(testingState).toEqual({
+            records: {
+                byId: {
+                    i1: {
+                        id: 'i1',
+                        name: '1',
+                        parentId: 'i2',
+                    },
+                    i2: {
+                        id: 'i2',
+                        name: '2',
+                    },
+                },
+            },
+        });
+
+        // data has been reached.
+        expect(selector(testingState, 'i1')).toEqual({
+            id: 'i1',
+            name: '1',
+            parentId: 'i2',
+            parent: {
+                id: 'i2',
+                name: '2',
+            },
+        });
+    });
+});
diff --git a/libs/ngrx-entity-relationship/src/lib/stateKeys.ts b/libs/ngrx-entity-relationship/src/lib/stateKeys.ts
index 57e118db0..b88d7601e 100644
--- a/libs/ngrx-entity-relationship/src/lib/stateKeys.ts
+++ b/libs/ngrx-entity-relationship/src/lib/stateKeys.ts
@@ -1,5 +1,22 @@
 import {ENTITY_STATE, ENTITY_STATE_CUSTOM, STORE_SELECTOR} from './types';
 
+export function stateKeys<
+    SELECTOR extends STORE_SELECTOR<any, any>,
+    STORE extends SELECTOR extends STORE_SELECTOR<infer U, any> ? U : never,
+    SLICE extends SELECTOR extends STORE_SELECTOR<any, infer U> ? U : never,
+    E_KEY extends keyof SLICE,
+    ENTITY extends SLICE extends ENTITY_STATE_CUSTOM<E_KEY, 'ids', infer U> ? U : never
+>(selector: SELECTOR, entitiesKey: E_KEY): STORE_SELECTOR<STORE, ENTITY_STATE<ENTITY>>;
+
+export function stateKeys<
+    SELECTOR extends STORE_SELECTOR<any, any>,
+    STORE extends SELECTOR extends STORE_SELECTOR<infer U, any> ? U : never,
+    SLICE extends SELECTOR extends STORE_SELECTOR<any, infer U> ? U : never,
+    E_KEY extends keyof SLICE,
+    I_KEY extends keyof SLICE,
+    ENTITY extends SLICE extends ENTITY_STATE_CUSTOM<E_KEY, I_KEY, infer U> ? U : never
+>(selector: SELECTOR, entitiesKey: E_KEY, idsKey: I_KEY): STORE_SELECTOR<STORE, ENTITY_STATE<ENTITY>>;
+
 export function stateKeys<
     SELECTOR extends STORE_SELECTOR<any, any>,
     STORE extends SELECTOR extends STORE_SELECTOR<infer U, any> ? U : never,
@@ -7,11 +24,11 @@ export function stateKeys<
     E_KEY extends keyof SLICE,
     I_KEY extends keyof SLICE,
     ENTITY extends SLICE extends ENTITY_STATE_CUSTOM<E_KEY, I_KEY, infer U> ? U : never
->(selector: SELECTOR, entitiesKey: E_KEY, idsKey: I_KEY): STORE_SELECTOR<STORE, ENTITY_STATE<ENTITY>> {
+>(selector: SELECTOR, entitiesKey: E_KEY, idsKey?: I_KEY): STORE_SELECTOR<STORE, ENTITY_STATE<ENTITY>> {
     const callback: STORE_SELECTOR<STORE, ENTITY_STATE<ENTITY>> = (s: STORE): ENTITY_STATE<ENTITY> => {
         const slice = selector(s);
         return {
-            ids: slice[idsKey],
+            ids: idsKey ? slice[idsKey] : slice.ids,
             entities: slice[entitiesKey],
         };
     };
diff --git a/libs/ngrx-entity-relationship/src/lib/types.ts b/libs/ngrx-entity-relationship/src/lib/types.ts
index 701fdb673..3e61eecdb 100644
--- a/libs/ngrx-entity-relationship/src/lib/types.ts
+++ b/libs/ngrx-entity-relationship/src/lib/types.ts
@@ -30,11 +30,11 @@ export type ENTITY_STATE_CUSTOM<EK extends keyof any, IK extends keyof any, ENTI
     };
 } &
     {
-        [key in IK]: Array<ID_TYPES>;
+        [key in IK]?: Array<ID_TYPES>;
     };
 
 export interface ENTITY_STATE<E> {
-    ids: Array<ID_TYPES>;
+    ids?: Array<ID_TYPES>;
     entities: {
         [id in ID_TYPES]?: E;
     };