为用户获取产品的数量- MongoDB，MongoDB，Node.js

Question

如何从users方案中获取用户名及其products产品的数量

产品:

{
 _id : ObjectId(5ab548d8bea65e21c413766f),
 userid: 5ab425c6f5bff145304092f7,
 product_name: "aaa",
 __v:0
},{
 _id: ObjectId(5ab7daa92ade533790268f48),
 userid: 5ab655bbb94733156c438112,
 product_name: "bbb",
 __v:0
},{
 _id: ObjectId(5aba43ef0a5c243330237bd5),
 userid: 5ab425c6f5bff145304092f7,
 product_name: "ccc",
 __v:0
}

用户:

{
 _id: ObjectId(5ab425c6f5bff145304092f7),
 username:"cccc",
 email:"cccc@gmail.com",
 __v:0
},{
 _id:ObjectId(5ab655bbb94733156c438112),
 username:"rrrr",
 email:"rrrr",
 __v:0
}

我希望结果如下：

    [ { _id: { username: 'rrrr' } , count: 1},
      { _id: { username: 'cccc' } , count: 2} ]

现在，我从这个开始：

products.aggregate([

  {$lookup:{
    from: "users",
    localField: "ObjectId(userid)",
    foreignField: "ObjectId(_id)",
    as: "users"
  }},
  {"$group" : {_id:{userid:"$userid" }, count:{$sum:1} } }

  ], function(err, result) {
      console.log(result);
      if(err){ res.status(400).json({ success: false, message:'Error processing request '+ err }); }
          res.status(201).json({
            success: true,
            data: result
      });  
    }
  );

脚本返回以下值：

[ { _id: { userid: '5ab655bbb94733156c438112' }, count: 1 },
  { _id: { userid: '5ab425c6f5bff145304092f7' }, count: 2 } ]

字段用户I同意，但我希望您在这里具有用户名属性。如何修改剧本？

Answer 1

您可以使用$last获取分组用户single data，并且可以显示它。

products.aggregate([

  {$lookup:{
    from: "users",
    localField: "ObjectId(userid)",
    foreignField: "ObjectId(_id)",
    as: "users"
  }},

{ "$group" :
  {
    _id: { userid: "$userid" },
    usrname: { $last: "$users.username" } ,
    count: { $sum: 1 }
  }
},

  ], function(err, result) {

      if(err){ res.status(400).json({ success: false, message:'Error processing request '+ err }); }
          res.status(201).json({
            success: true,
            data: result
      });  
    }
  );
}

你可以在这里找到文档

Answer 2

溶液

products.aggregate([

  {$lookup:{
    from: "users",
    localField: "ObjectId(userid)",
    foreignField: "ObjectId(_id)",
    as: "users"
  }},

{ "$group" :
  {
    _id: { userid: "$userid" },
    name: { $last: "$users.username" } ,
    count: { $sum: 1 }
  }
}, {$sort: {"_id.userid":  1}}

  ], function(err, result) {

      if(err){ res.status(400).json({ success: false, message:'Error processing request '+ err }); }
          res.status(201).json({
            success: true,
            data: result
      });  
    }
  );
}