aggregation

const getPreferencesForLoggedinUser = async (req) => {
  let userId = req.userData.userId;
  let result = await Preference.aggregate([
    { $match: { user: mongoose.Types.ObjectId(userId) } },
    {
      $lookup: {
        from: Keyword.collection.name,
        localField: "keyword",
        foreignField: "_id",
        as: "keywordData",
      },
    },
    { $unwind: "$keywordData" },
    {
      $project: {
        _id: 0,
        keyword: "$keywordData.keyword",
        user: 1,
      },
    },
    {
      $group: {
        _id: "$user",
        keywords: {
          $push: "$keyword",
        },
      },
    },
    {
      $project: {
        _id: 0,
        user: "$_id",
        keywords: 1,
      },
    },
  ]);
  return result;
};