fix(queryCursor): add _transformForAsyncIterator transform after user-defined transforms

Fix mongoosejs/mongoose-lean-getters#44

Author: vkarpov15

lib/cursor/queryCursor.js

@@ -77,6 +77,9 @@ function QueryCursor(query) {
     if (this.options.transform) {
       this._transforms.push(this.options.transform);
     }
+    if (this._mongooseOptions._transformForAsyncIterator) {
+      this._transforms.push(_transformForAsyncIterator);
+    }
     // Re: gh-8039, you need to set the `cursor.batchSize` option, top-level
     // `batchSize` option doesn't work.
     if (this.options.batchSize) {
@@ -396,9 +399,7 @@ QueryCursor.prototype.transformNull = function(val) {
  */
 
 QueryCursor.prototype._transformForAsyncIterator = function() {
-  if (this._transforms.indexOf(_transformForAsyncIterator) === -1) {
-    this.map(_transformForAsyncIterator);
-  }
+  this._mongooseOptions._transformForAsyncIterator = true;
   return this;
 };
 

test/query.test.js

@@ -2354,6 +2354,19 @@ describe('Query', function() {
     assert.strictEqual(called, 1);
   });
 
+  it('transform with for/await and cursor', async function() {
+    const Model = db.model('Test', new Schema({ name: String }));
+
+    await Model.create({ name: 'test' });
+    const cursor = Model.find().transform(doc => doc?.name.toUpperCase() ?? null).cursor();
+    const names = [];
+    for await (const name of cursor) {
+      names.push(name);
+    }
+
+    assert.deepStrictEqual(names, ['TEST']);
+  });
+
   describe('orFail (gh-6841)', function() {
     let Model;