How To Populate objects inside array through aggregation

Working with Data
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2

Hi @Ahmed_Abdelrahman,

This can be done by first $unwinding the orderItems array, using a $lookup against the products collection, replacing the product field then re-$grouping the results.

For example:

// setup
db.products.insert({
  _id: ObjectId('61c5e1e7c2ec39450cdf41b7'),
  name: 'lorem ipsum dolor set',
  image: '1452877_product.png',
  type: 'immo file',
  price: 20
});
db.orders.insertMany([{
  _id: ObjectId('61c45d25bdf9c1389879db9f'),
  orderItems: [{
    options: [{
      _id: ObjectId('61fd914d4a236b94f816c27d'),
      question: 'lorem ipsum dolor set amet',
      answer: 'lorem'
    }, {
      _id: ObjectId('61fd914d4a236b94f816c27d'),
      question: 'lorem ipsum dolor set amet',
      answer: 'lorem'
    }, {
      _id: ObjectId('61fd914d4a236b94f816c27d'),
      question: 'lorem ipsum dolor set amet',
      answer: 'lorem'
    }, {
      _id: ObjectId('61fd914d4a236b94f816c27d'),
      question: 'lorem ipsum dolor set amet',
      answer: 'lorem'
    }, ],
    quantity: 4,
    product: ObjectId('61c5e1e7c2ec39450cdf41b7')
  }, {
    options: [{
        _id: ObjectId('61fd914d4a236b94f816c27d'),
        question: 'lorem ipsum dolor set amet',
        answer: 'lorem'
      }, {
        _id: ObjectId('61fd914d4a236b94f816c27d'),
        question: 'lorem ipsum dolor set amet',
        answer: 'lorem'
      },
      {
        _id: ObjectId('61fd914d4a236b94f816c27d'),
        question: 'lorem ipsum dolor set amet',
        answer: 'lorem'
      }, {
        _id: ObjectId('61fd914d4a236b94f816c27d'),
        question: 'lorem ipsum dolor set amet',
        answer: 'lorem'
      },
    ],
    quantity: 3,
    product: ObjectId('61c5e1e7c2ec39450cdf41b7')
  }]
}])

// aggregate
db.orders.aggregate([
{ $unwind: "$orderItems" },
{ $lookup: {
   from: "products",
   localField: "orderItems.product",
   foreignField: "_id",
   as: "product"
}},
{ $set: {
  "orderItems.product": "$product"
}},
{ $group: {
  _id: "$_id",
  orderItems: { $push: "$orderItems" }
}}  
])

The above example is for the mongo/mongosh shell, but could be adapted to work in Node.js if it works for your use case.

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