$push/$addToSet
Reference group: Accumulators and ranking
What it does
Collects values; $addToSet deduplicates, $push preserves duplicates.
Syntax
Array accumulator expressions
Use case
Collect related IDs.
Important notes
Large arrays can consume memory and produce oversized documents.
$push/$addToSet: practical example
{ $group: { _id: "$customerId", statuses: { $addToSet: "$status" }, orderIds: { $push: "$_id" } } }💡 Explanation
Collects values;
$addToSet deduplicates, $push preserves duplicates.
When to use it
Collect related IDs.
Caution
Large arrays can consume memory and produce oversized documents.Key Takeaways
- Collects values;
$addToSetdeduplicates,$pushpreserves duplicates. - Typical use: Collect related IDs.