perf(NODE-5906): optimize toArray to use batches

src/cursor/abstract_cursor.ts

@@ -297,6 +297,7 @@ export abstract class AbstractCursor<
 
     return bufferedDocs;
   }
+
   async *[Symbol.asyncIterator](): AsyncGenerator<TSchema, void, void> {
     if (this.isClosed) {
       return;
@@ -457,9 +458,24 @@ export abstract class AbstractCursor<
    * cursor.rewind() can be used to reset the cursor.
    */
   async toArray(): Promise<TSchema[]> {
-    const array = [];
+    const array: TSchema[] = [];
+
+    // when each loop iteration ends,documents will be empty and a 'await (const document of this)' will run a getMore operation
     for await (const document of this) {
       array.push(document);
+      let docs = this.readBufferedDocuments();
+      if (this.transform != null) {
+        docs = await Promise.all(
+          docs.map(async doc => {
+            if (doc != null) {
+              return await this.transformDocument(doc);
+            } else {
+              throw Error;
+            }
+          })
+        );
+      }
+      array.push(...docs);
     }
     return array;
   }

test/integration/node-specific/abstract_cursor.test.ts

@@ -5,6 +5,7 @@ import { Transform } from 'stream';
 import { inspect } from 'util';
 
 import {
+  AbstractCursor,
   type Collection,
   type FindCursor,
   MongoAPIError,
@@ -361,4 +362,37 @@ describe('class AbstractCursor', function () {
       });
     });
   });
+
+  describe('toArray', () => {
+    let nextSpy;
+    let client: MongoClient;
+    let cursor: AbstractCursor;
+    let col: Collection;
+    const numBatches = 10;
+    const batchSize = 4;
+
+    beforeEach(async function () {
+      client = this.configuration.newClient();
+      col = client.db().collection('test');
+      await col.deleteMany({});
+      for (let i = 0; i < numBatches; i++) {
+        await col.insertMany([{ a: 1 }, { a: 2 }, { a: 3 }, { a: 4 }]);
+      }
+      nextSpy = sinon.spy(AbstractCursor.prototype, 'next');
+    });
+
+    afterEach(async function () {
+      sinon.restore();
+      await cursor.close();
+      await client.close();
+    });
+
+    it('iterates per batch not per document', async () => {
+      cursor = client.db().collection('test').find({}, { batchSize });
+      await cursor.toArray();
+      expect(nextSpy.callCount).to.equal(numBatches + 1);
+      const numDocuments = numBatches * batchSize;
+      expect(nextSpy.callCount).to.be.lessThan(numDocuments);
+    });
+  });
 });