enhance: Schemas with no entities should not infer (#323)

packages/rest-hooks/src/react-integration/__tests__/useResource.tsx

@@ -391,7 +391,7 @@ describe('useResource()', () => {
     const { result, waitForNextUpdate } = renderRestHook(() => {
       return useResource(photoShape, { userId });
     });
-    expect(result.current).toBe(null);
+    expect(result.current).toBe(undefined);
     await waitForNextUpdate();
     expect(result.current).toStrictEqual(response);
   });

packages/rest-hooks/src/state/selectors/__tests__/useDenormalized.ts

@@ -4,6 +4,7 @@ import {
   NestedArticleResource,
   UserResource,
   IndexedUserResource,
+  photoShape,
 } from '__tests__/common';
 import { normalize, NormalizedIndex } from 'rest-hooks/resource';
 import { initialState } from 'rest-hooks/state/reducer';
@@ -164,7 +165,7 @@ describe('useDenormalized()', () => {
       });
     });
 
-    describe.only('no result exists but index is used when using nested schema', () => {
+    describe('no result exists but index is used when using nested schema', () => {
       const pageArticle = PaginatedArticleResource.fromJS({
         ...params,
         author: 23,
@@ -590,6 +591,30 @@ describe('useDenormalized()', () => {
       });
     });
 
+    it('should not infer with schemas that have no entities', () => {
+      const userId = '5';
+      const { result } = renderHook(() => {
+        return useDenormalized(photoShape, { userId }, initialState as any);
+      });
+      expect(result.current).toStrictEqual([undefined, true]);
+    });
+
+    it('should return results as-is for schemas with no entities', () => {
+      const userId = '5';
+      const results = new ArrayBuffer(10);
+      const state = {
+        ...initialState,
+        results: {
+          ...initialState.results,
+          [photoShape.getFetchKey({ userId })]: results,
+        },
+      };
+      const { result } = renderHook(() => {
+        return useDenormalized(photoShape, { userId }, state);
+      });
+      expect(result.current).toStrictEqual([results, true]);
+    });
+
     it('should throw with invalid schemas', () => {
       const shape = PaginatedArticleResource.listShape();
       shape.schema = { happy: { go: { lucky: 5 } } } as any;

packages/rest-hooks/src/state/selectors/useDenormalized.ts

@@ -5,7 +5,7 @@ import {
   DenormalizeNullable,
   ParamsFromShape,
 } from 'rest-hooks/resource';
-import { isEntity } from '@rest-hooks/normalizr';
+import { isEntity, Schema } from '@rest-hooks/normalizr';
 import { useMemo } from 'react';
 
 import hasUsableData from '../../react-integration/hooks/hasUsableData';
@@ -47,8 +47,16 @@ export default function useDenormalized<
   }, [cacheResults, state.indexes, serializedParams]);
   // TODO: only update when relevant indexes change
 
+  const needsDenormalization = useMemo(() => schemaHasEntity(schema), [schema]);
+
   // Compute denormalized value
   const [denormalized, entitiesFound, entitiesList] = useMemo(() => {
+    if (!needsDenormalization)
+      return [cacheResults, true, ''] as [
+        DenormalizeNullable<Shape['schema']>,
+        any,
+        string,
+      ];
     // Warn users with bad configurations
     /* istanbul ignore next */
     if (process.env.NODE_ENV !== 'production' && isEntity(schema)) {
@@ -98,6 +106,7 @@ export default function useDenormalized<
     serializedParams,
     results,
     expired,
+    needsDenormalization,
     options && options.invalidIfStale,
   ]);
 
@@ -108,3 +117,19 @@ export default function useDenormalized<
     entitiesList,
   ]);
 }
+
+/** Determine whether the schema has any entities.
+ *
+ * Without entities, denormalization is not needed, and results should not be inferred.
+ */
+function schemaHasEntity(schema: Schema): boolean {
+  if (isEntity(schema)) return true;
+  if (Array.isArray(schema) && schema.length) return schemaHasEntity(schema[0]);
+  if (schema && typeof schema === 'object' && !('denormalize' in schema)) {
+    return Object.values(schema).reduce(
+      (prev, cur) => prev || schemaHasEntity(cur),
+      false,
+    );
+  }
+  return false;
+}