从两个数据库集合（Mongoose/MongoDB）中查询和匹配

Posted 2023-03-11

【中文标题】从两个数据库集合（Mongoose/MongoDB）中查询和匹配

【英文标题】：Query and Match from Two Database Collections (Mongoose/MongoDB)

【发布时间】：2021-09-27 23:06:09

【问题描述】：

我需要帮助创建一个 mongoose 查询，该查询在用户集合中找到请求用户的喜欢，然后在帖子集合中搜索用户的喜欢。希望有人能告诉我我在查询中做错了什么，或者我怎样才能做得更好。

用户和帖子集合：

const users = [

  _id: "1",
  likes: ["1", "2"]
,

  _id: "2",
  likes: ["3"]

]

const posts = [

  _id: "1",
  stuff: "stuff1"
,

  _id: "2",
  stuff: "stuff2"
,

  _id: "3",
  stuff: "stuff3"

]

聚合查询：

router.post("/", authUser, async (req, res) => 
  User.aggregate([
    
      $match: 
        _id: ObjectId(req.user._id), //user 1
      ,
    ,
    
      $unwind: "$likes",
    ,
    
      $lookup: 
        from: "posts",
        let:  like: "$likes" ,
        pipeline: [
          
            $match: 
              $expr: 
                $eq: ["_id", "$$like"],
              ,
            ,
          ,
        ],
        as: "matched_posts",
      ,
    ,
    
      $unwind: "$matched_posts",
    ,
  ]).then((d) => 
    console.log(d);
  );
);

期望的输出：

const output = [

  _id: "1",
  stuff: "stuff1"
,

  _id: "2",
  stuff: "stuff2"

]

【参考方案1】：

$match你的条件 $lookup 与帖子集合，传递 likes 作为 localField 和 _id 作为 foreignField $unwind解构likes数组 $replaceRoot 替换 likes 对象

router.post("/", authUser, async (req, res) => 
  User.aggregate([
     $match:  _id: ObjectId(req.user._id)  ,
    
      $lookup: 
        from: "posts",
        localField: "likes",
        foreignField: "_id",
        as: "likes"
      
    ,
     $unwind: "$likes" ,
     $replaceRoot:  newRoot: "$likes"  
  ])
  .then((d) => 
    console.log(d);
  );
);

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