mongoose 只给出子文档的_id 时如何查询子文档？

Question

我在数据库中有一个文档的快照，如下所示

{
        "_id" : ObjectId("624e105df043d4ad4ee893ee"),
        "title" : "First post",
        "author" : "Rituparna",
        "comments" : [
                {
                        "content" : "First comment",
                        "author" : "Ritu",
                        "_id" : ObjectId("624e109b966fbe64b2a80ea9"),
                        "replies" : [ ]
                },
                {
                        "content" : "second comment",
                        "author" : "Ritu",
                        "_id" : ObjectId("624e10a4e33f7962d0002f39"),
                        "replies" : [ ]
                }
        ],
        "__v" : 0
}

现在假设你只得到一个评论的_id，说第一个评论624e109b966fbe64b2a80ea9

我要找的最终结果是

{
    "content" : "First comment",
    "author" : "Ritu",
    "_id" : ObjectId("624e109b966fbe64b2a80ea9"),
    "replies" : [ ]
}

当我只得到评论的 _id 和 Post 模型（子文档模型的父模型）时，我需要编写什么查询？

Answer 1

db.collection.aggregate([
  {
    $match: { "comments._id": ObjectId("624e109b966fbe64b2a80ea9") }
  },
  {
    $unwind: "$comments"
  },
  {
    $match: { "comments._id": ObjectId("624e109b966fbe64b2a80ea9") }
  },
  {
    $replaceWith: "$comments"
  }
])

https://mongoplayground.net/p/WmeoKTg8tUS