Mongo DB query

query.js

db.getCollection('playlists').aggregate([
    { $unwind: '$videos' },
    {
      $lookup: {
        from: 'videos',
        let: { videoId: '$videos' },
        pipeline: [
          { $match: { $expr: { $and: [{ $eq: ['$_id', '$$videoId'] }] } } },
          {
            $lookup: {
              from: 'tags',
              localField: 'tags',
              foreignField: '_id',
              as: 'tags'
            }
          },
          { $project: { tags: 1 } },
          { $unwind: '$tags' }
        ],
        as: 'videos'
      }
    },
    { $unwind: { path: '$videos', preserveNullAndEmptyArrays: true } },
    {
      $group: {
        _id: { _id: '$_id', title: '$title' },
        videos: { $addToSet: '$videos._id' },
        tags: { $addToSet: '$videos.tags.label' }
      }
    },
    {
      $project: {
        _id: '$_id._id',
        title: '$_id.title',
        videos: '$videos',
        tags: '$tags'
      }
    },
    { $match: { tags: { $in: ['mongo', 'node'] } } }
  ]);