feat(QueryCursor): add getDriverCursor() function that returns the ra…

…w driver cursor

lib/cursor/queryCursor.js

@@ -10,6 +10,7 @@ const eachAsync = require('../helpers/cursor/eachAsync');
 const helpers = require('../queryHelpers');
 const kareem = require('kareem');
 const immediate = require('../helpers/immediate');
+const { once } = require('node:events');
 const util = require('util');
 
 /**
@@ -135,6 +136,25 @@ QueryCursor.prototype._read = function() {
   });
 };
 
+/**
+ * Returns the underlying cursor from the MongoDB Node driver that this cursor uses.
+ *
+ * @method getDriverCursor
+ * @memberOf QueryCursor
+ * @returns {Cursor} MongoDB Node driver cursor instance
+ * @instance
+ * @api public
+ */
+
+QueryCursor.prototype.getDriverCursor = async function getDriverCursor() {
+  if (this.cursor) {
+    return this.cursor;
+  }
+
+  await once(this, 'cursor');
+  return this.cursor;
+};
+
 /**
  * Registers a transform function which subsequently maps documents retrieved
  * via the streams interface or `.next()`

test/query.cursor.test.js

@@ -900,6 +900,25 @@ describe('QueryCursor', function() {
     assert.ok(err);
     assert.ok(err.message.includes('skipMiddlewareFunction'), err.message);
   });
+
+  it('returns the underlying Node driver cursor with getDriverCursor()', async function() {
+    const schema = new mongoose.Schema({ name: String });
+
+    const Movie = db.model('Movie', schema);
+
+    await Movie.deleteMany({});
+    await Movie.create([
+      { name: 'Kickboxer' },
+      { name: 'Ip Man' },
+      { name: 'Enter the Dragon' }
+    ]);
+
+    const cursor = await Movie.find({}).cursor();
+    assert.ok(!cursor.cursor);
+    const driverCursor = await cursor.getDriverCursor();
+    assert.ok(cursor.cursor);
+    assert.equal(driverCursor, cursor.cursor);
+  });
 });
 
 async function delay(ms) {