I am trying to sending the response of specific object from subdocument array of objects

[masud_hasn]

this is the document where i have a sub document as cartItems.

i want send the specific object as response from this cart item array.

but when i am using aggregate i am getting the empty array as response.

this is my controller part. i tried in two ways for my expected response.

exports.getSingleItem = async (req, res) => {
  const { itemId } = req.params
  const { email } = req.user

  const targetUser = await User.findOne({ email }).exec()
  const singleItem = await Cart.aggregate([
    {
      $match: {
        user: targetUser.id,
      },
    },
    {
      $replaceRoot: {
        newRoot: {
          $first: {
            $filter: {
              input: '$cartItems',
              as: 'item',
              cond: {
                $eq: ['$$item._id', itemId],
              },
            },
          },
        },
      },
    },
  ])
  res.json(singleItem)
}

this is the secound way which i tried.

const isCartExist = await Cart.aggregate([
  {
    $match: {
      ' user': targetUser._id,
    },
  },
  {
    $unwind: '$cartItems',
  },
  {
    $match: {
      'cartItems._id': itemId,
    },
  },
  {
    $replaceRoot: {
      newRoot: '$cartItems',
    },
  },
]).exec((err, item) => {
  if (err) {
    console.log(err)
  } else {
    res.json(item)
    console.log(item)
  }
})