MongoDB query profiling

Capture every Mongoose query and aggregation and inspect them in the MongoDB panel.

This tutorial shows how to add the Mongoose collector to profile MongoDB queries in a NestJS application that uses @nestjs/mongoose.

Prerequisites

@eleven-labs/nest-profiler installed and configured
@nestjs/mongoose and mongoose installed with a working MongooseModule connection

Step 1 — Install the package

pnpm add @eleven-labs/nest-profiler-mongoose

Step 2 — Register the collector

Add MongooseCollectorModule in the feature module that performs MongoDB operations:

reviews/reviews.module.ts

import { MongooseModule } from '@nestjs/mongoose';
import { MongooseCollectorModule } from '@eleven-labs/nest-profiler-mongoose';

@Module({
  imports: [
    MongooseModule.forFeature([{ name: Review.name, schema: ReviewSchema }]),
    MongooseCollectorModule.forRoot({
      slowQueryThreshold: 50, // queries > 50ms highlighted (default: 100)
    }),
  ],
})
export class ReviewsModule {}

The collector injects the Connection automatically via @InjectConnection().

Step 3 — Instrument your services with spans

import { ProfilerService } from '@eleven-labs/nest-profiler';

@Injectable()
export class ReviewsService {
  constructor(
    @InjectModel(Review.name) private readonly model: Model<ReviewDocument>,
    private readonly profiler: ProfilerService,
  ) {}

  async findAll(): Promise<ReviewDocument[]> {
    const stop = this.profiler.startSpan('mongo.reviews.findAll');
    const result = await this.model.find().sort({ createdAt: -1 }).exec();
    stop();
    return result;
  }

  async getStats() {
    const stop = this.profiler.startSpan('mongo.reviews.aggregate');
    const result = await this.model
      .aggregate([
        { $match: { status: 'approved' } },
        { $group: { _id: '$productId', avgRating: { $avg: '$rating' } } },
      ])
      .exec();
    stop();
    return result;
  }
}

Step 4 — Test it

curl -i http://localhost:3000/reviews

Copy the X-Debug-Token header, open /_profiler/{token}, and click the MongoDB tab.

You will see:

Each query with its operation badge (find, aggregate, …)
Collection name
Filter object
Duration per query
Slow queries highlighted in red
Result count for find queries

How it works

The collector patches mongoose.Query.prototype.exec and mongoose.Aggregate.prototype.exec on the Mongoose instance obtained from connection.base. This captures:

All Model.find(), Model.findOne(), Model.findById() queries
All Model.updateOne(), Model.deleteOne(), Model.deleteMany() mutations
All Model.aggregate() pipelines
Model.countDocuments(), Model.distinct(), and other cursor-based operations

Queries executed outside a request context (e.g., during module initialization or seeding) are silently ignored since there is no active CLS profile.

Anti-double-patch guard

If multiple modules import MongooseCollectorModule.forRoot(), the patch is applied only once — a __profilerPatched flag prevents double-wrapping Query.prototype.exec.