$expr
Reference group: Query filter operators
What it does
Allows aggregation expressions inside query filters.
Syntax
{$expr: expression}
Use case
Compare fields in one document.
$expr: practical example
db.inventory.find({ $expr: { $lt: ["$available", "$reorderPoint"] } })💡 Explanation
Allows aggregation expressions inside query filters.
When to use it
Compare fields in one document.
Key Takeaways
- Allows aggregation expressions inside query filters.
- Typical use: Compare fields in one document.