我需要左反加入 mongodb 与查找和匹配聚合函数

Question

我想在 MongoDB

中转换此查询

Select * 来自不存在的问题（select * 来自 Solved_question 其中 questionid = id 和 username=username）

集合架构

question:{ 
    _id:ObjectId,
    title:String,
    desc:string, 
    Author:string
 },
       
 User:{
    _id:ObjectId, 
    Email:string,
    Password:string
 },
Solvedquestioncollection:{
 Id:_id,
 QuestionId:{ type:mongoose.Schema.ObjectId, ref:"Question" },
 UserId:{ type:mongoose.Schema.ObjectId, ref:"User" } 
}

示例文档

Question:[
{
 _id:ObjectId('1'),
title:"main component of computer",
desc:"some desc for this"
author:"ashick"
},
{
 _id:ObjectId('2'),
title:"Advantage of CPU",
desc:"some desc for this"
author:"ashick"
},
]

User:[
{
_id:ObjectId('1'),
email:"as@g.com",
password:"12345"
},
{
_id:ObjectId('2'),
email:"df@g.com",
password:"345"
}
]
solvedquestion:[
{
_id:ObjectId('1'),
question:ObjectId('2'),
userId:ObjectId('1')
},
{
_id:ObjectId('2'),
question:ObjectId('2'),
userId:ObjectId('2')
}
]

我想在问题集中获取特定用户没有解决的问题

我试试这个

question = await Question.aggregate([
        {
          $lookup: {
            from: "solvedquestions",
            let: { userId: "$userId" },
            pipeline: [
              {
                $match: {
                  $expr: {
                    $eq: ["ObjectId('60ebc6b9980b8e1f8cffe34b'"), "$$userId"],
                  },
                },
              },
            ],
            as: "resultingArray",
          },
        },
        
      ]);

但它的 Return 空数组

感谢您的回答

Answer 1

try {
let aggregate = Question.aggregate([
     {
          $lookup: {
            from: 'solvedquestions',
            let: {
              question_id: '$_id',
              question_userId: '$user'
            },
            pipeline: [ {
              $match: {
                $expr: {
                  $and: [
                    {
                      $eq: ['$QuestionId', '$$question_id']
                    },
                    {
                      $eq: ['$userId', '$$question_userId']
                    }
                  ]
                }
              }
            }],
            as: 'results'
          }
        }
]);
 return await aggregate.exec();
} catch (error) {
  console.error('Error ->',error);
}

希望对您有所帮助，如有任何疑问，请告诉我。乐于助人:)

我需要左反加入 mongodb 与查找和匹配聚合函数

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