What are MongoDB aggregation pipelines in Node.js?

What are MongoDB aggregation pipelines in Node.js?

MongoDB aggregation pipelines are a framework for data processing and transformation in MongoDB. They allow you to process data records and return computed results. In Node.js, you can use the MongoDB driver to build and execute these pipelines.

Can you give me an example of an aggregation pipeline?

Sure! An example of an aggregation pipeline is using the $match stage to filter documents, followed by the $group stage to group the results. For instance, you can filter orders by a specific date and then group them by customer ID to get the total sales per customer.

How do I implement this in my Node.js application?

To implement it, first, ensure you have the MongoDB Node.js driver installed. Then, you can create a pipeline array with your stages and use the aggregate() method on your collection. Here's a simple example:

const pipeline = [
  { $match: { date: { $gte: new Date('2023-01-01') } } },
  { $group: { _id: '$customerId', totalSales: { $sum: '$amount' } } }
];

collection.aggregate(pipeline).toArray((err, results) => {
  if (err) throw err;
  console.log(results);
});

What are some common stages used in aggregation pipelines?

Common stages include $match, $group, $sort, $project, and $lookup. Each stage serves a specific purpose, like filtering, grouping, sorting, reshaping documents, or joining collections.