Enhance regSub function to support string-based computeFn for direct field access in appdb, and add corresponding tests for new functionality.

Author: flexsurfer

src/subs.ts

@@ -14,14 +14,18 @@ import { mergeTrace, withTrace } from './trace';
 const KIND = 'sub';
 const KIND_DEPS = 'subDeps';
 
-export function regSub<R>(id: Id, computeFn?: (...values: any[]) => R, depsFn?: (...params: any[]) => SubVector[]): void {
+export function regSub<R>(id: Id, computeFn?: ((...values: any[]) => R) | string, depsFn?: (...params: any[]) => SubVector[]): void {
     if (hasHandler(KIND, id)) {
         consoleLog('warn', `[reflex] Overriding. Subscription '${id}' already registered.`)
     }
     // If only id is provided, use root subscription logic
     if (!computeFn) {
         registerHandler(KIND, id, () => getAppDb()[id])
         registerHandler(KIND_DEPS, id, () => [])
+    } else if (typeof computeFn === 'string') {
+        // String field subscription - access field directly from appdb
+        registerHandler(KIND, id, () => getAppDb()[computeFn])
+        registerHandler(KIND_DEPS, id, () => [])
     } else {
         // Computed subscriptions require depsFn
         if (!depsFn) {

src/tests/hook.test.tsx

@@ -13,6 +13,7 @@ describe('React Hooks', () => {
   // Register test subscriptions
   regSub('user');
   regSub('user-name', (user) => user?.name, () => [['user']]);
+  regSub('user-email-str', 'userEmail'); // Test string computeFn - simple field name
   regSub('todos');
   regSub('todos-count', (todos) => (todos || []).length, () => [['todos']]);
 
@@ -23,6 +24,7 @@ describe('React Hooks', () => {
         name: 'John Doe',
         email: '[email protected]'
       },
+      userEmail: '[email protected]', // For string-based subscription test
       todos: [
         { id: 1, text: 'Test todo', completed: false }
       ]
@@ -63,6 +65,12 @@ describe('React Hooks', () => {
       expect(result.current).toBe(1);
     });
 
+    it('should return string-based subscription value', () => {
+      const { result } = renderHook(() => useSubscription(['user-email-str']));
+
+      expect(result.current).toBe('[email protected]');
+    });
+
     it('should handle subscription with parameters', () => {
       // Register a parameterized subscription
       regSub('todo-by-id', (todos, id) => {