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$reverseArray

The $reverseArray operator returns a new array with the elements in reverse order.

📌 Syntax

{ "$reverseArray": <arrayExpression> }

✅ Base Example – Reverse Numbers

📥 Input Document

{ "nums": [1, 2, 3, 4, 5] }

📌 Expression

{ "$reverseArray": "$nums" }

📤 Output

[5, 4, 3, 2, 1]

✅ Base Example – Reverse Strings

📥 Input Document

{ "tags": ["new", "sale", "exclusive"] }

📌 Expression

{ "$reverseArray": "$tags" }

📤 Output

["exclusive", "sale", "new"]

🧱 Ecommerce Example – Show Most Recent Orders First

📌 Pipeline

[
  {
    "$project": {
      "customer": "$name",
      "recentOrders": {
        "$reverseArray": "$orders"
      }
    }
  }
]

📥 Input Document

{
  "name": "Alice",
  "orders": [
    { "orderId": 1, "amount": 50 },
    { "orderId": 2, "amount": 75 },
    { "orderId": 3, "amount": 30 }
  ]
}

📤 Output

{
  "customer": "Alice",
  "recentOrders": [
    { "orderId": 3, "amount": 30 },
    { "orderId": 2, "amount": 75 },
    { "orderId": 1, "amount": 50 }
  ]
}

🔧 Common Use Cases

  • Display latest entries first
  • Change processing order
  • Use before slicing or accessing via index
  • $slice, $arrayElemAt, $map, $concatArrays

🧠 Notes

  • Input must be an array; otherwise returns null.
  • Does not modify the original array.