我有一个集合“产品”，另一个集合“交易”，然后是“用户”。每种产品都有一些交易，每笔交易都有一个用户。所以我想获取产品......

我有一个集合“产品”、另一个集合“交易”以及“用户”。每种产品都有一些交易，而每笔交易都有一个用户。因此，我想从用户集合中获取具有交易键值对的产品，其中包含基于产品 ID 的数组，然后每个交易都包含基于旅行者 ID 的旅行者键值对。

如果存在一些交易，则我已实现所需的输出，但如果没有交易，则它不会返回交易：[]，而是返回交易：[{}]

我正在运行这个查询：

const tripProducts = await db.collection('products')
                .aggregate([
                    { $match: { tripId: new ObjectId(tripId ?? '') } },
                    { $lookup: { from: 'transactions', localField: '_id', foreignField: 'productId', as: 'transactions' } },
                    { $unwind: { path: '$transactions', preserveNullAndEmptyArrays: true } }, // Unwind transactions array
                    { $lookup: { from: 'users', localField: 'transactions.travellerId', foreignField: '_id', as: 'traveller' } },
                    { $unwind: { path: '$traveller', preserveNullAndEmptyArrays: true } }, // Unwind traveller array
                    { $addFields: { 'transactions.traveller': '$traveller' } },
                    {
                        $group: {
                            _id: '$_id',
                            // Include all fields from products using $first or similar operators
                            tripId: { $first: '$tripId' },
                            name: { $first: '$name' },
                            category: { $first: '$category' },
                            productPrice: { $first: '$productPrice' },
                            currency: { $first: '$currency' },
                            depositForBusiness: { $first: '$depositForBusiness' },
                            depositDate: { $first: '$depositDate' },
                            finalDate: { $first: '$finalDate' },
                            minTravellers: { $first: '$minTravellers' },
                            maxTravellers: { $first: '$maxTravellers' },
                            amount: { $first: '$amount' },
                            depositAmount: { $first: '$depositAmount' },
                            platformFeeForDeposit: { $first: '$platformFeeForDeposit' },
                            platformFee: { $first: '$platformFee' },
                            userId: { $first: '$userId' },
                            transactions: { $push: '$transactions' } // Push the transactions with the traveller details
                        }
                    }
                ])
                .toArray();

我的输出是：

[
    {
        "_id": "66d62cb0caeb8c9e204a10b5",
        "tripId": "66d62bc5caeb8c9e204a10b3",
        "name": "Next Year",
        "category": " Stay",
        "productPrice": 10000,
        "currency": "usd",
        "depositForBusiness": 1000,
        "depositDate": "2024-09-04T19:00:00.000Z",
        "finalDate": "2025-04-09T19:00:00.000Z",
        "minTravellers": 1,
        "maxTravellers": 2,
        "amount": 10975.6,
        "depositAmount": 1098.1,
        "platformFeeForDeposit": 98.1,
        "platformFee": 975.6000000000004,
        "userId": "66bb9220366e6c4942f4943e",
        "transactions": [
            {}
        ]
    },
    {
        "_id": "66d73682b976159272117780",
        "tripId": "66d62bc5caeb8c9e204a10b3",
        "name": "Tomorrow",
        "category": " Stay",
        "productPrice": 1000,
        "currency": "dkk",
        "depositForBusiness": 100,
        "depositDate": "2024-09-03T19:00:00.000Z",
        "finalDate": "2024-09-03T19:00:00.000Z",
        "minTravellers": 1,
        "maxTravellers": 2,
        "amount": 1098.1,
        "depositAmount": 110.35,
        "platformFeeForDeposit": 10.35,
        "platformFee": 98.09999999999991,
        "userId": "66bb9220366e6c4942f4943e",
        "transactions": [
            {}
        ]
    }
]