feat(dataset): add collectAllKeys option for full CSV export (#2945)

packages/core/src/storages/dataset.ts

@@ -170,6 +170,11 @@ export interface DatasetIteratorOptions
 export interface DatasetExportToOptions extends DatasetExportOptions {
     fromDataset?: string;
     toKVS?: string;
+    /**
+     * If true, includes all unique keys from all dataset items in the CSV export.
+     * If omitted or false, only keys from the first item are used.
+     */
+    collectAllKeys?: boolean;
 }
 
 /**
@@ -349,7 +354,16 @@ export class Dataset<Data extends Dictionary = Dictionary> {
         const items = await this.export(options);
 
         if (contentType === 'text/csv') {
-            const keys = Object.keys(items[0]);
+            // To handle empty dataset exports gracefully.
+            if (items.length === 0) {
+                await kvStore.setValue(key, '', { contentType });
+                return items;
+            }
+
+            const keys = options?.collectAllKeys
+                ? Array.from(new Set(items.flatMap(Object.keys)))
+                : Object.keys(items[0]);
+
             const value = stringify([
                 keys,
                 ...items.map((item) => {

test/core/storages/dataset.test.ts

@@ -550,6 +550,28 @@ describe('dataset', () => {
                 const kvData = await KeyValueStore.getValue('TEST-123-123-csv');
                 expect(kvData).toEqual('hello,foo\nworld 1,bar 1\nworld 2,bar 2\nworld 3,bar 3\n');
             });
+            it('should export all fields when collectAllKeys is true', async () => {
+                const dataset = await Dataset.open();
+                await dataset.pushData([
+                    { id: 1, name: 'Alice' },
+                    { id: 2, age: 30 },
+                ]);
+
+                const kvStore = await KeyValueStore.open();
+                await dataset.exportTo(
+                    'test.csv',
+                    {
+                        toKVS: kvStore.name,
+                        collectAllKeys: true,
+                    },
+                    'text/csv',
+                );
+
+                const exported = await kvStore.getValue('test.csv');
+                expect(exported).toContain('id');
+                expect(exported).toContain('name');
+                expect(exported).toContain('age');
+            });
         });
     });
 });