{
    "_id" : ObjectId("5ad5ddb15e540442a7d4213c"),
    "updatedAt" : ISODate("2018-05-09T10:13:24.107Z"),
    "createdAt" : ISODate("2018-04-17T11:42:41.027Z"),
    "title" : "111111111111111111111111111111",
    "content" : "222222222222222222222222222222222222222222",
    "author" : ObjectId("5ac8ba3582c2345af70d4658"),
    "comments" : [
        ObjectId("5af2a10dc56ad8378a3fbffa"),
        ObjectId("5af2a87b370d32a64d34efb4")
    ],
    "images" : [],
    "__v" : 0
}

{
    "_id" : ObjectId("5af2a10dc56ad8378a3fbffa"),
    "likeBy" : [
        ObjectId("5ac8ba3582c2345af70d4658")
    ],
    "dislikeBy" : [],
    "author" : ObjectId("5ac8ba3582c2345af70d4658"),
    "post" : ObjectId("5ad5ddb15e540442a7d4213c"),
    "comment" : "222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222",
    "type" : "post",
    "createdAt" : ISODate("2018-05-09T07:19:41.895Z"),
    "updatedAt" : ISODate("2018-05-09T10:13:08.431Z"),
    "__v" : 0
}
{
    "_id" : ObjectId("5af2a87b370d32a64d34efb4"),
    "likeBy" : [],
    "dislikeBy" : [
        ObjectId("5ac8ba3582c2345af70d4658")
    ],
    "author" : ObjectId("5ac8ba3582c2345af70d4658"),
    "post" : ObjectId("5ad5ddb15e540442a7d4213c"),
    "comment" : "444444444444444444444444",
    "type" : "post",
    "createdAt" : ISODate("2018-05-09T07:19:41.895Z"),
    "updatedAt" : ISODate("2018-05-09T10:13:12.087Z"),
    "__v" : 0
}

{
    "_id" : ObjectId("5ac8ba3582c2345af70d4658"),
    "firstName" : "Bruce",
    "lastName" : "Wayne",
    "email" : "[email protected]"
}

const post = await Post.aggregate([
          { $match: { _id: mongoose.Types.ObjectId(id) }},
          { $lookup: {
              from: 'comments',
              localField: 'comments',
              foreignField: '_id',
              as: 'comments'
            }
          },
          { $lookup: {
              from: 'users',
              localField: 'author',
              foreignField: '_id',
              as: 'author'
            }
          },
          { $unwind: '$author' },
          { $unwind: '$comments' },
          { $addFields: {
            "comments.isLiked": {
              $in: [
                mongoose.Types.ObjectId(req.user.id),
                "$comments.likeBy"
              ]
            },
            "comments.isDisliked": {
              $in: [
                mongoose.Types.ObjectId(req.user.id),
                "$comments.dislikeBy"
              ]
            },
              "comments.likeByCount": { $size: '$comments.likeBy' },
              "comments.dislikeByCount": { $size: '$comments.dislikeBy' }
          }},
          { $lookup: {
              from: 'users',
              localField: 'comments.author',
              foreignField: '_id',
              as: 'comments.author'
            }
          },
          { $unwind: '$comments.author' },
          { $group: {
              _id: '$_id',
              updatedAt: {$first: '$updatedAt'},
              createdAt: {$first: '$createdAt'},
              title: {$first: '$title'},
              content: {$first: '$content'},
              author: {$first: '$author'},
              comments: {$push: '$comments'},
              images: {$first: '$images'}
            }
          },
          { $project: {
              updatedAt: 1, createdAt: 1, title: 1, content: 1, author: '$author', comments: 1, images: 1
            }
          }
        ])