MongoDB/Aggregation

The aggregation framework lets MongoDB process documents through a pipeline of stages. You can filter records, reshape documents, group values, calculate totals, sort results, join related collections, and perform many other transformations directly inside the database.

Each stage takes the output from the previous stage and passes a new set of documents to the next one. Learning how to design efficient pipelines is important because aggregation can perform complex data processing without requiring your application to fetch every document and process it itself.