具有 3 个级别的 MongoDB 嵌套查找并将新值附加到结果文档

Question

我需要从数据库中检索整个单个对象层次结构作为 JSON。实际上，关于实现此结果的任何其他解决方案的建议将受到高度评价。我决定使用具有 $lookup 支持的 MongoDB。

所以我有四个收藏：

1. 用户

{ "_id" : "2", "name" : "john" }
{ "_id" : "1", "name" : "Doe" }

1. 帖子

{"_id": "2","body": "hello", likes: []},
{"_id": "1","name": "hello 4", likes: [1,]},

1. 评论

{"_id": "c2","body": "hello 3",postId: "1",likes: [1,2]},
{"_id": "c1","body": "hello 2",postId: "1",likes: [1,2]},

1. 回复

{"_id": "r1","name": "hello 4",commentId: "c1",likes: [1]},
{"_id": "r3","name": "hello five",commentId: "c2",likes: [1,2]}

我基本上需要检索所有带有所有相应 cmets 和 cmets.replies 的帖子作为我的结果的一部分。我的聚合：

  const posts = await PostModel.aggregate([
      {
        $lookup: {
          from: "comments",
          localField: "_id",
          foreignField: "postId",
          as: "comments",
        },
      },
      {
        $unwind: "$comments",
      },
      {
        $lookup: {
          from: "replies",
          localField: "comments._id",
          foreignField: "commentId",
          as: "comments.replies",
        },
      },
    ]).sort({
      createdAt: -1,
    });

MongoDb PlayGround

结果很奇怪。有些记录没问题。但是 cmets 返回一个对象。 _id="1" 的帖子也有一些重复。

[
  {
    "_id": "1",
    "comments": {
      "_id": "c2",
      "body": "hello 3",
      "likes": [
        1,
        2
      ],
      "postId": "1",
      "replies": [
        {
          "_id": "r3",
          "commentId": "c2",
          "likes": [
            1,
            2
          ],
          "name": "hello five"
        }
      ]
    },
    "likes": [
      1
    ],
    "name": "hello 4"
  },
  {
    "_id": "1",
    "comments": {
      "_id": "c1",
      "body": "hello 2",
      "likes": [
        1,
        2
      ],
      "postId": "1",
      "replies": [
        {
          "_id": "r1",
          "commentId": "c1",
          "likes": [
            1
          ],
          "name": "hello 4"
        }
      ]
    },
    "likes": [
      1
    ],
    "name": "hello 4"
  }
]

简而言之，这是我的预期结果。

• 我想获取所有帖子，以及与之关联的所有 cmets 和回复。
• 我想添加一个喜欢的计数likesCount:{$size:["likes"]}，因为我已经准备好用户身份验证 ID(uid)，我想根据isLiked: {$in:[ID(uid),"likes"]} 来检查用户是否喜欢该帖子、评论或回复

Answer 1

由于每个帖子都有多个 cmets，展开 cmets 后需要将它们组合在一起形成一个数组

更新 我已经更新了 fetch 方法，如下所示。

  db.posts.aggregate([
  {
    $lookup: {
      from: "comments",
      localField: "_id",
      foreignField: "postId",
      as: "comments",
      
    },
    
  },
  {
    $unwind: "$comments",
    
  },
  {
    $lookup: {
      from: "replies",
      localField: "comments._id",
      foreignField: "commentId",
      as: "replies",
      
    },
    
  },
  {
    $unwind: "$replies",
    
  },
  {
    "$addFields": {
      "replies.countOflikes": {
        $size: {
          $ifNull: [
            "$replies.likes",
            []
          ]
        }
      },
      "replies.isLiked": {
        $cond: {
          if: {
            $eq: [
              {
                $size: {
                  $filter: {
                    input: "$replies.likes",
                    as: "item",
                    cond: {
                      $eq: [
                        "$$item",
                        1//id of the user whom you wanna check if liked the reply
                        
                      ]
                    }
                  }
                }
              },
              0
            ]
          },
          then: false,
          else: true
        }
      }
    }
  },
  {
    $group: {
      _id: "$comments._id",
      postId: {
        $first: "$_id"
      },
      body: {
        $first: "$body"
      },
      "comments": {
        $first: "$comments"
      },
      replies: {
        $push: "$replies"
      }
    }
  },
  {
    $addFields: {
      "comments.replies": "$replies"
    }
  },
  {
    $group: {
      _id: "$postId",
      body: {
        $first: "$body"
      },
      comments: {
        $push: "$comments"
      }
    }
  }
])

变更摘要

1. 展开两个 cmets 及其回复
2. 添加了用于显示 isLiked 和 countOfLikes 的新字段，使用 addFields 舞台
3. 两次分组以改造数据的原始结构（先按 cmets 分组，然后按帖子分组）

https://mongoplayground.net/p/lymCfeIIy9j