我如何计算每个类别的考试

如何解决我如何计算每个类别的考试

我有 3 个集合。一种用于类别，一种用于考试，一种用于结果。类别如下：

{
  _id: 3276438964823,name: 'Category 1',companyId: 12345
}

试卷如下：

{
  _id: 482348327,categoryId: 3276438964823,name: "Computer",companyId: 12345
}

结果集合如下：

{
  _id: 482348327,exam_id: 482348327
}

我想要的结果是这样的：

[
  {category: 'Categori 1',exam_count: 1,exam_done: 0},{category: 'Categori 2',exam_count: 8,exam_done: 5},.....
]

现在我已经尝试过这个代码：

Exams.aggregate([
    {
      $match: {
        companyId: { $in: 
            [mongoose.Types.ObjectId(req.userData.companyId)] },},{
      $lookup: {
        from: "categories",let: {
          companyid: "$companyId",pipeline: [
          {
            $match: {
              $expr: {
                $and: [
                  {
                    $eq: ["$companyId","$$companyid"],{
                    $eq: ["$type",1],],{
            $project: {
              _id: 1,name: 1,}
          }
        ],as: "categories",])

我现在得到的是这个：

[
{
    "_id": "5ee366cb3fd50f3d388493ac","active": 1,"categoryId": "5eb640414ac4b84d944a3639","name": "Test 2","insertDate": "2020-06-12T11:28:11.966Z","__v": 0,"companyId": "5f621c2461090c2f40a014d3","categories": [
        {
            "_id": "5f621d3e61090c2f40a014d9","name": "A1,A2,B1,B"
        },{
            "_id": "5f621d4b61090c2f40a014db","name": "C1,C"
        }
    ]
},{
    "_id": "5f5d2eea4387a83088e6f802","categoryId": "5f5cf44710cd434344b36a91","insertDate": "2020-09-12T20:26:18.294Z",]

但这不是我想要的。我想统计我的类别集合中所有类别的所有考试

解决方法

您正在从考试集合中查询并使用类别查找，但它应该从类别和查找中使用考试，

$lookup 与 exams 集合
$lookup 与 results 集合
$addFeilds 使用 $size

Categories.aggregate([
  {
    $lookup: {
      from: "exams",localField: "_id",foreignField: "categoryId",as: "examsCount"
    }
  },{
    $lookup: {
      from: "results",localField: "examsCount._id",foreignField: "exam_id",as: "doneExams"
    }
  },{
    $addFields: {
      examsCount: { $size: "$examsCount" },doneExams: { $size: "$doneExams" }
    }
  }
])

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