$merge
Reference group: Pipeline stages
What it does
Writes pipeline results into a target collection.
Syntax
{$merge: { into, on?, whenMatched?, whenNotMatched? }}
Use case
Maintain materialized summaries.
Important notes
Plan idempotency and target indexes.
$merge: practical example
{ $merge: { into: "customerSummaries", on: "_id", whenMatched: "merge", whenNotMatched: "insert" } }💡 Explanation
Writes pipeline results into a target collection.
When to use it
Maintain materialized summaries.
Caution
Plan idempotency and target indexes.
Key Takeaways
- Writes pipeline results into a target collection.
- Typical use: Maintain materialized summaries.