$objectToArray

The $objectToArray operator converts a document (object) into an array of key-value pair documents.

---

📌 Syntax

{ "$objectToArray": <documentExpression> }

Each entry in the output array has the form:

{ "k": <key>, "v": <value> }

---

✅ Base Example – Convert Object to Array

📥 Input Document

{ "data": { "x": 1, "y": 2 } }

📌 Expression

{ "$objectToArray": "$data" }

📤 Output

[
  { "k": "x", "v": 1 },
  { "k": "y", "v": 2 }
]

---

🧱 Ecommerce Example – Flatten Dynamic Properties

📌 Pipeline

[
  {
    "$project": {
      "product": "$name",
      "attributes": {
        "$objectToArray": "$customAttributes"
      }
    }
  }
]

📥 Input Document

{
  "name": "Sneakers",
  "customAttributes": {
    "size": "10",
    "color": "Red",
    "style": "Casual"
  }
}

📤 Output

{
  "product": "Sneakers",
  "attributes": [
    { "k": "size", "v": "10" },
    { "k": "color", "v": "Red" },
    { "k": "style", "v": "Casual" }
  ]
}

---

🔧 Common Use Cases

• Transform object keys into documents
• Use with $map and $filter on object properties
• Enable custom aggregation logic for dynamic keys

---

🔗 Related Operators

• $arrayToObject, $getField, $setField, $mergeObjects

---

🧠 Notes

• Input must be an object; returns error on arrays or null
• Often paired with $map or $reduce for key-based logic

---