fix: toJSON with belongsTo Assoication (#287)

packages/database/src/__tests__/model.test.ts

@@ -0,0 +1,60 @@
+import { Database, mockDatabase } from '@nocobase/database';
+
+describe('model', () => {
+  let db: Database;
+
+  beforeEach(async () => {
+    db = mockDatabase();
+  });
+
+  afterEach(async () => {
+    await db.close();
+  });
+
+  describe('toJSON', () => {
+    it('should return null when belongsTo association empty', async () => {
+      const user = db.collection({
+        name: 'users',
+        fields: [
+          { type: 'string', name: 'name' },
+          { type: 'hasMany', name: 'posts' },
+        ],
+      });
+
+      const posts = db.collection({
+        name: 'posts',
+        fields: [
+          {
+            type: 'string',
+            name: 'title',
+          },
+          {
+            type: 'belongsTo',
+            name: 'user',
+          },
+        ],
+      });
+
+      await db.sync();
+
+      const u1 = await db.getRepository('users').create({
+        values: {
+          name: 'u1',
+        },
+      });
+
+      await db.getRepository('posts').create({
+        values: {
+          title: 'p1',
+        },
+      });
+
+      const p1 = await db.getRepository('posts').findOne({
+        appends: ['user'],
+      });
+
+      const p1JSON = p1.toJSON();
+      expect(p1JSON['user']).toBeNull();
+    });
+  });
+});

packages/database/src/model.ts

@@ -70,7 +70,7 @@ export class Model<TModelAttributes extends {} = any, TCreationAttributes extend
           if (['HasMany', 'BelongsToMany'].includes(association.associationType)) {
             result[key] = handleArray(data[key], opts).map((item) => traverseJSON(item, opts));
           } else {
-            result[key] = traverseJSON(data[key], opts);
+            result[key] = data[key] ? traverseJSON(data[key], opts) : null;
           }
         } else {
           result[key] = data[key];