$project

Reshapes documents by including, excluding, or computing fields.

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Syntax

{ "$project": { "<field>": <0|1|expression>, ... } }

• Set a field to 1 to include it, 0 to exclude it.
• Provide an expression to compute a new value (aliasing is allowed by assigning to a new field name).
• _id is included by default; set "_id": 0 to drop it.

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✅ Basic Example

📌 Stage

{
  "$project": {
    "product": 1,
    "price": 1,
    "_id": 0
  }
}

📥 Input

{
  "product": "Laptop",
  "price": 1200,
  "internal": true
}

📤 Output

{
  "product": "Laptop",
  "price": 1200
}

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🧱 Deep Nested Pipeline Usage (Ecommerce)

[
  {
    "$unwind": "$items"
  },
  {
    "$project": {
      "item": "$items.name",
      "cost": "$items.price"
    }
  }
]

📥 Input Document

{
  "orderId": 1,
  "items": [
    {
      "name": "Phone",
      "price": 500
    },
    {
      "name": "Case",
      "price": 30
    }
  ]
}

📤 Output Documents

[
  {
    "item": "Phone",
    "cost": 500
  },
  {
    "item": "Case",
    "cost": 30
  }
]

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➕ Supported Accumulators

None for this stage

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🔧 Common Operators

$literal, $ifNull, $toUpper

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