mongo查询联接-从另一个集合中获取总记录作为键

如何解决mongo查询联接-从另一个集合中获取总记录作为键

我有两个收藏夹：

quiz_customer_record 集合

user(id,status_id)

虚拟收藏

{
    "_id" : ObjectId("5f6ec91cbf74d27430b9c24f"),"quiz_id" : "5f3a33185a1cd35632b8c98c","user_id" : "5efae8bed5c5f06f30a057ff","name" : "ABC","qualification" : "ttt","time_required" : "0:13 Mins","questions_attempted" : 2,"total_quiz_questions" : 2,"attempt_date" : "2020-09-26T04:52:48.169Z"
}

/* 4 */
{
    "_id" : ObjectId("5f6eca82bf74d27430b9c252"),"user_id" : "5f6ec9ba3b502398598a5ade","name" : "Test","qualification" : "BSC","time_required" : "0:6 Mins","attempt_date" : "2020-09-26T04:58:46.060Z"
}

从第二个（虚拟集合中，我希望每个用户获得总记录）

我正在使用需要修改的查询：

/* 1 */
{
    "_id" : ObjectId("5f6ec906bf74d27430b9c24d"),"question_id" : "5f6ec888bf74d27430b9c248","selected_answer" : [ 
        "rgdfgdfg"
    ],"attempt_date" : "2020-09-26T04:52:25.977Z","correct_answer" : [ 
        "rgdfgdfg"
    ],"result" : true
}

/* 2 */
{
    "_id" : ObjectId("5f6eca82bf74d27430b9c250"),"attempt_date" : "2020-09-26T04:58:46.060Z","result" : true
}

/* 3 */
{
    "_id" : ObjectId("5f6eca82bf74d27430b9c251"),"question_id" : "5f6ec8b4bf74d27430b9c24b","selected_answer" : [ 
        "sdfsdf"
    ],"correct_answer" : [ 
        "sdfsdf"
    ],"result" : true
}

这将给出如下结果：

 db.quiz_customer_record.aggregate([{ $match: { quiz_id:"5f3a33185a1cd35632b8c98c"}},{
        $sort: { attempt_date: -1 }
    },{
        $group: {
            _id: "$user_id",result1: { $first: "$attempt_date" },quiz_id: { $first: "$quiz_id" },o_id: { $first: "$_id" }
        }
    },{
        $project: {
            _id: "$o_id",user_id: "$_id",result1: 1
        }
    }
])

预期结果：（根据/* 1 */ { "attempt_date" : "2020-09-26T04:52:48.169Z","_id" : ObjectId("5f6ec91cbf74d27430b9c24f"),"user_id" : "5efae8bed5c5f06f30a057ff" } /* 2 */ { "attempt_date" : "2020-09-26T04:58:46.060Z","_id" : ObjectId("5f6eca82bf74d27430b9c252"),"user_id" : "5f6ec9ba3b502398598a5ade" } ，我需要虚拟集合中user_id和quiz_id（上述查询的结果1）匹​​配的记录数）

attempt_date

其中/* 1 */ { "attempt_date" : "2020-09-26T04:52:48.169Z","total_dummy_rec":0 } /* 2 */ { "attempt_date" : "2020-09-26T04:58:46.060Z","total_dummy_rec":2 } 是“虚拟”集合中每个用户的总记录数。

我对如何处理感到困惑，因此我可以实现此结果。帮我找到解决方案。谢谢！

解决方法

您可以在管道阶段之后添加2个阶段，

• $lookup加入dummy集合，其中在let和管道匹配条件下传递必填字段
• 最后移动了$project，并使用$size
计算了虚拟文档的总数

  {
    $lookup: {
      from: "dummy",let: {
        quiz_id: "$quiz_id",user_id: "$_id",attempt_date: "$attempt_date"
      },pipeline: [
        {
          $match: {
            $expr: {
              $and: [
                { $eq: ["$$quiz_id","$quiz_id"] },{ $eq: ["$$user_id","$user_id"] },{ $eq: ["$$attempt_date","$attempt_date"] }
              ]
            }
          }
        }
      ],as: "dummy"
    }
  },{
    $project: {
      _id: "$o_id",result1: 1,total_dummy_rec: {
        $size: "$dummy"
      }
    }
  }

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