aggregation: Add automatic _id mapping in aggregation cursors #81

src/client.ts

@@ -4,6 +4,7 @@ import * as fastDeepEqual from 'fast-deep-equal/es6';
 import * as _ from 'lodash';
 import * as mingo from 'mingo';
 import {
+	AggregationCursor,
 	ClientSession,
 	Collection,
 	Db,
@@ -1062,16 +1063,24 @@ export class N9MongoDBClient<U extends BaseMongoObject, L extends BaseMongoObjec
 		options?: CollectionAggregationOptions,
 		readInOutputCollection: boolean = false,
 	): N9AggregationCursor<T> {
+		let nativeCursor: AggregationCursor;
+		let collection: Collection<U>;
 		if (readInOutputCollection) {
-			const nativeCursor = this.collection.aggregate<T>(aggregateSteps, options);
-			return new N9AggregationCursor<T>(this.collection, nativeCursor, aggregateSteps);
+			nativeCursor = this.collection.aggregate<T>(aggregateSteps, options);
+			collection = this.collection;
+		} else {
+			nativeCursor = this.collectionSourceForAggregation.aggregate<T>(aggregateSteps, options);
+			collection = this.collectionSourceForAggregation;
 		}
-		const nativeCursor = this.collectionSourceForAggregation.aggregate<T>(aggregateSteps, options);
-		return new N9AggregationCursor<T>(
-			this.collectionSourceForAggregation,
-			nativeCursor,
-			aggregateSteps,
-		);
+		return new N9AggregationCursor<T>(collection, nativeCursor, aggregateSteps).map((doc: T) => {
+			if (
+				typeof (doc as any)?._id === 'object' &&
+				(doc as any)._id.constructor.name === 'ObjectId' // faster than instanceof check
+			) {
+				(doc as any)._id = (doc as any)._id.toHexString();
+			}
+			return doc;
+		});
 	}
 
 	public aggregateWithBuilder<T = void>(

test/aggregation-cursor.test.ts

@@ -2,7 +2,6 @@ import test, { ExecutionContext } from 'ava';
 import * as _ from 'lodash';
 
 import { BaseMongoObject, N9AggregationCursor, N9MongoDBClient } from '../src';
-import { ObjectId } from '../src/mongodb';
 import { getBaseMongoClientSettings, getOneCollectionName, init, TestContext } from './fixtures';
 
 class SampleType extends BaseMongoObject {
@@ -62,8 +61,7 @@ test('[Cursor] iterate using while hasNext ... next', async (t: ExecutionContext
 		items2.push(item);
 	}
 	t.is(items2.length, 5, 'cursor contains 5 items read with hasNext and next');
-	t.is(typeof items[0]._id, 'object', '_id is an object, aggregation results are not mapped');
-	t.true((items[0]._id as any) instanceof ObjectId, '_id is an ObjectId');
+	t.is(typeof items[0]._id, 'string', '_id is a string, aggregation results are mapped');
 
 	t.deepEqual(items2, items, 'compare two arrays');
 });
@@ -119,7 +117,7 @@ test('[Cursor] Check cursor map function : should change data', async (t: Execut
 		.aggregate<SampleType>([{ $sort: { field1String: 1 } }])
 		.map((sampleType) => ({
 			// type of sampleType should be deduced automatically
-			_id: sampleType._id.toString(),
+			_id: sampleType._id,
 			somethingElse: sampleType.field1String,
 		}));
 	const items: { somethingElse: string; _id: string }[] = [];
@@ -140,6 +138,44 @@ test('[Cursor] Check cursor map function : should change data', async (t: Execut
 	}
 });
 
+test('[Cursor] Check _id automatic mapping, should leave objects', async (t: ExecutionContext<ContextContent>) => {
+	const cursor: N9AggregationCursor<{
+		_id: {
+			value: number;
+			prop2: number;
+		};
+	}> = t.context.mongoClient.aggregate<any>([
+		{
+			$group: {
+				_id: 1,
+			},
+		},
+		{
+			$project: {
+				_id: {
+					value: '$_id',
+					prop2: {
+						$sum: ['$_id', '$_id'],
+					},
+				},
+			},
+		},
+	]);
+
+	t.is(await cursor.count(), 1, 'check cursor length');
+	const doc = await cursor.next();
+	t.deepEqual(
+		doc,
+		{
+			_id: {
+				value: 1,
+				prop2: 2,
+			},
+		},
+		'_id is an object',
+	);
+});
+
 test('[Cursor] Check cursor map function : should be chainable', async (t: ExecutionContext<ContextContent>) => {
 	const cursor = t.context.mongoClient
 		.aggregate<SampleType>([{ $sort: { field1String: 1 } }])