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What does "aggregation pipeline" mean?

MongoDBJunior~1 min read
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An aggregation pipeline is a data-processing conveyor in MongoDB, where documents pass through a sequence of stages, each one transforming the data step by step: filtering, sorting, grouping, projecting, and so on.

The key ideas

  1. A pipeline is a chain of stages Data flows top to bottom, like through pipes. One stage's output is the next stage's input.
  2. Every stage does one clear thing For example:
  • $match, a filter
  • $group, grouping and aggregates
  • $sort, sorting
  • $project, picking and changing fields
  1. Everything happens on MongoDB's side So you're not pulling a lot of data into your code, you're processing it right inside the DB, which is faster and more efficient.

Example

js
db.orders.aggregate([ { $match: { status: "paid" } }, { $group: { _id: "$user_id", total: { $sum: "$amount" } } }, { $sort: { total: -1 } } ]);
  • first a filter by status
  • then a sum per user
  • then sorting by the total

Summary

An aggregation pipeline is a mechanism where data passes through a chain of stages, gets transformed step by step, and produces a finished analytical result in a single query.

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