蒙戈DB选择所有行的FOM根据连接条件

Question

2代表我有2个表

useraverage 
    id 
    average 



usersdetails 
    id 
    name 
    address 

output 
id 
name 
address 
average 

我试图查找，但它不是返回数据。

db.userdetails.aggregate([ 
    { 
     $lookup: 
     { 
      from: "useraverage", 
      localField: "id", 
      foreignField: "id", 
      as: "useraverage" 
     } 
    } 
    ],function (err, result) { 
     console.log(result); 
     res.json(result); 
    }); 

Answer 1

你使用的是MongoDB的_id还是你自己的？如果您使用第一个选项，那么你查询应该是这样的：

 
    `db.userdetails.aggregate([ 
    { 
     $lookup: 
     { 
      from: "useraverage", 
      localField: "_id", 
      foreignField: "_id", 
      as: "useraverage" 
     } 
    }, 
    {$unwind : "$useraverage"}, 
    {$project : { 
     name : 1, 
     address : 1, 
     average: "$useraverage.average" 
     }} 
    ],function (err, result) { 
     console.log(result); 
     res.json(result); 
    });`