Aggregation stages
An aggregation stage represents a specific step in the pipeline where the data transformation process takes place. Each stage processes data and outputs documents that can be further processed by the subsequent stages.
Let's explore some key stages that act as the building blocks of a pipeline:
$match
: Use$match
to filter the documents so that only those that meet the specified condition(s) are passed to the next pipeline stage. This stage should be used early in the pipeline, because filtering out unnecessary documents leads to processing only the relevant documents in the following stages, leading to significant performance improvements.Example: Find all users older than 22.
Input
[ { "_id": 1, "name": "Alice", "age": 21 }, { "_id": 2, "name": "Bob", "age": 25 }, { "_id": 3, "name": "Charlie", "age...