MongoDB's aggregation framework processes documents through pipeline stages. Each stage transforms the document stream. Complex analytics, grouping, and reshaping happen efficiently server-side.
Pipeline Stages
$match filters documents early. $group aggregates by keys. $project shapes output fields. $lookup joins collections. $unwind flattens arrays. Combine stages for complex transformations.
- Use $match early to reduce documents processed
- Group and aggregate with $group and accumulators
- Reshape documents with $project and $addFields
- Join collections using $lookup for related data
- Optimize pipelines by checking explain output
Performance Optimization
Index fields used in $match and $sort stages. Place $match early filtering documents before expensive operations. Limit fields projected reducing memory usage. Consider using views for reusable aggregations.