Mongoose Profiling Middleware

1.0.2 verified Thu Apr 23 auth: no javascript

mongoose-profiling-middleware is a utility package for Node.js applications that integrates with Mongoose to leverage MongoDB's native profiling capabilities. It automatically injects the current source file and line number as a `$comment` into every Mongoose query executed against a MongoDB instance. This feature allows developers to easily identify the exact code location responsible for slow or frequent database operations when analyzing the MongoDB `system.profile` collection. The current stable version, 1.0.2, offers a straightforward, side-effect-based integration. This middleware simplifies the process of identifying performance bottlenecks by automating query annotation, distinguishing it from manual comment insertion. Its primary function is to provide immediate context for database query performance, thereby aiding optimization efforts without requiring significant application code changes.

Common errors

error Queries in `system.profile` do not have a `$comment` field, or show 'undefined:undefined'. ↓

cause The `mongoose-profiling-middleware` was not loaded, or it was loaded before Mongoose schemas were fully defined and registered.

fix

Ensure require('mongoose-profiling-middleware'); is placed in your code *after* mongoose.connect() has been called and your Mongoose models have been defined.

error No entries are found in the `system.profile` collection, or it contains unrelated entries. ↓

cause MongoDB's database profiling level is not enabled or is set to `0` (off) for the database being used.

fix

In a MongoDB shell, connect to your database and run db.setProfilingLevel(1) to profile slow operations, or db.setProfilingLevel(2) to profile all operations. Remember to set the level for the correct database.

Warnings

gotcha Enabling profiling in MongoDB (db.setProfilingLevel(1) or db.setProfilingLevel(2)) can introduce a marginal performance overhead on your database server. It is crucial to monitor its impact, especially in production environments. ↓

fix Profile in controlled environments first. When profiling in production, monitor database performance metrics closely and disable profiling when not actively debugging.

gotcha This middleware automatically adds `$comment` fields to your Mongoose queries. If your application or other middleware already utilizes the `$comment` field for other purposes, there might be conflicts or unexpected behavior as it will be overwritten. ↓

fix Review existing Mongoose queries and middleware to ensure they do not rely on a custom `$comment` field if you intend to use this profiling middleware.

gotcha The profiling middleware must be `require`d or `import`ed *after* Mongoose has been connected to MongoDB and any relevant Mongoose schemas and models have been defined. If loaded too early, it may not correctly intercept all queries. ↓

fix Place `require('mongoose-profiling-middleware');` immediately after `mongoose.connect()` completes and before your application starts making database queries.

Install

npm install mongoose-profiling-middleware

yarn add mongoose-profiling-middleware

pnpm add mongoose-profiling-middleware

Imports

Side-effect import (CommonJS)
wrong
```
const profiler = require('mongoose-profiling-middleware');
```
correct
```
require('mongoose-profiling-middleware');
```
This package operates purely as a side-effect middleware and does not export any symbols for direct use. It must be required AFTER Mongoose is initialized and schemas are defined for proper function.
Side-effect import (ESM)
wrong
```
import profiler from 'mongoose-profiling-middleware';
```
correct
```
import 'mongoose-profiling-middleware';
```
For ESM environments, use a direct side-effect import. Like CommonJS, this import should occur after Mongoose connection and schema setup.

Quickstart

This quickstart demonstrates how to set up Mongoose, load the profiling middleware, and execute several Mongoose operations that will be annotated with source code comments for MongoDB profiling.

const mongoose = require('mongoose');

async function run() {
  try {
    await mongoose.connect('mongodb://localhost:27017/myprofiledb', {
      useNewUrlParser: true,
      useUnifiedTopology: true,
    });
    console.log('MongoDB connected.');

    const MySchema = new mongoose.Schema({
      name: String,
      value: Number,
    });
    const MyModel = mongoose.model('MyItem', MySchema);

    // IMPORTANT: Require the middleware AFTER mongoose is connected and models are defined.
    require('mongoose-profiling-middleware');

    console.log('Mongoose profiling middleware loaded.');
    console.log('To see profiling data, ensure you run: db.setProfilingLevel(1) or db.setProfilingLevel(2) in your mongo shell for the "myprofiledb" database.');

    // Perform some Mongoose operations that will be profiled
    await MyModel.create({ name: 'TestItemA', value: 100 });
    await MyModel.findOne({ name: 'TestItemA' });
    await MyModel.updateOne({ name: 'TestItemA' }, { value: 200 });
    await MyModel.find({});
    await MyModel.deleteOne({ name: 'TestItemA' });

    console.log('Example Mongoose operations completed. Check the system.profile collection in MongoDB for details.');

  } catch (error) {
    console.error('Error during Mongoose operations:', error);
  } finally {
    await mongoose.disconnect();
    console.log('MongoDB disconnected.');
  }
}

run();