Flatten MongoDB nested object-CodePudding

I have a collection which looks like this:

[
    {
        productId: 'c69b7701-c33f-4801-99f3-080450f2b6c7',
        createdAt: '2021-12-04T17:33:34.221Z',
        history: [{
            value: 304,
            storePrice: 50,
            date: 1638639214000,
            prevSold: {
                price: 303,
                createdAt: '2021-12-04T17:32:50.658Z',
            },
        },
            ...100   more records,
        ],
        _id: '61aba66d9085f0044f96a700',
    }, ...100   more records,
];

And I'm just calling it with a basic find ie:

const slug = req.params.slug

ProductPrice.find({ productId: slug}).exec((err, data) => {
    if (err){
        return res.status(400).json({
            error: errorHandler(err)
        })
    }
    res.json(data)
})

I need to get the prev sold price into the same level as history.value

ie:

[
    {
        productId: 'c69b7701-c33f-4801-99f3-080450f2b6c7',
        createdAt: '2021-12-04T17:33:34.221Z',
        history: [{
            value: 304,
            storePrice: 50,
            date: 1638639214000,
            prevSold: 303,
        },
            ...100   more records,
        ],
        _id: '61aba66d9085f0044f96a700',
    },
    ...100   more records,
];

So far I've tried the following aggregate call but it's just returning an empty array. Can anyone point me in the right direction please?

ProductPrice.aggregate([
    { $match: { productId: slug } },
    { $unwind: '$history.prevSold' },
    {
        $addFields: {
            'prevSold.value': '$price',
        },
    },
    {
        $replaceRoot: {
            newRoot: '$prevSold',
        },
    },
]);

Thanks,

CodePudding user response：

Using an aggregation is the right way, here is a working example using $map:

db.collection.aggregate([
  {
    $addFields: {
      history: {
        $map: {
          input: "$history",
          in: {
            "$mergeObjects": [
              "$$this",
              {
                prevSold: "$$this.prevSold.price"
              }
            ]
          }
        }
      }
    }
  }
])

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