Matching Array Elements

Orders embed items. Each element is a document. A dotted path like items.unitPrice means some element has that field. Two dotted paths mean some element matches the first and some element matches the second — not necessarily the same one.

{
  userId: ObjectId("64a1b2c3d4e5f6a7b8c90001"),
  amount: 4900,
  status: "completed",
  items: [
    { name: "Mechanical Keyboard", quantity: 1, unitPrice: 4500 },
    { name: "USB-C Cable", quantity: 2, unitPrice: 200 }
  ]
}

db.orders.find({
  "items.unitPrice": { $gt: 500 },
  "items.quantity": 2
})

{ amount: 4900, items: [ { name: "Mechanical Keyboard", quantity: 1, unitPrice: 4500 }, { name: "USB-C Cable", quantity: 2, unitPrice: 200 } ] }

There is no line with unitPrice > 500 and quantity: 2. The filter still hits. That is normal array matching: each condition is independent across the array. If that is what you wanted (any expensive item, and separately any qty-2 item), you are done. If you wanted one line item that is both, you need $elemMatch — next lesson.

A single dotted condition is fine: { "items.name": "USB-C Cable" } — at least one item has that name. The bug appears when you AND two conditions on the array of objects.