Can you explain advanced examples of MongoDB aggregation pipelines in Node.js?

Can you explain advanced examples of MongoDB aggregation pipelines in Node.js?

Sure! The aggregation pipeline in MongoDB allows you to process data records and return computed results. For example, you can use stages like $match, $group, and $sort to filter, group, and sort your data.

Can you provide a specific example using $group?

Absolutely! Let's say you have a collection of orders. You can group them by customer ID and calculate the total amount spent by each customer using:

Order.aggregate([
  { $group: { _id: '$customerId', totalSpent: { $sum: '$amount' } } }
])

What if I want to filter the results to only include customers who spent over $100?

You can add a $match stage after the $group stage to filter the results. Here's how:

Order.aggregate([
  { $group: { _id: '$customerId', totalSpent: { $sum: '$amount' } } },
  { $match: { totalSpent: { $gt: 100 } } }
])

Can I sort the results by total spent in descending order?

Yes! You can add a $sort stage at the end of the pipeline:

Order.aggregate([
  { $group: { _id: '$customerId', totalSpent: { $sum: '$amount' } } },
  { $match: { totalSpent: { $gt: 100 } } },
  { $sort: { totalSpent: -1 } }
])