Using document field as JS object field-name in aggregation pipeline

Question

I have an JS object called tasksCountMap:

const tasksCountMap = {
   'Freshman': 46,
   'Senior': 10
}

and I need get count of task for each user type in my aggregation pipe, 'Freshman', 'Senior' it's document field called gradeLevel. I'm trying do it like this:

status: {
        $let: {
          vars: {
            tasksCount: tasksCountMap['$gradeLevel'],
            completedTasksCount: '$completedTasksCount[0].count'
          },
          in: {
            $cond: {
              if: { $or: [
                { $eq: ['$$tasksCount', '$$completedTasksCount'] },
                { $lte: ['$$tasksCount', '$$completedTasksCount'] },
              ]},
              then: 'On track',
              else: 'High priority'
            }
          }
        }
      }

Also '$completedTasksCount[0].count' doesn't work to...

Can someone show right way to do this?

All pipeline:

{
    $match: {
      type: 'student',
      counselorUserName: username
    },
    $project: {
      username: '$username',
      email: '$email',
      phone: '$phone',
      fullName: '$fullName',
      gradeLevel: {
        $switch: {
          branches: [{
              case: {
                $eq: ['$gradeLevel', '9']
              },
              then: 'Freshman'
            },
            {
              case: {
                $eq: ['$gradeLevel', '10']
              },
              then: 'Sophomore'
            },
            {
              case: {
                $eq: ['$gradeLevel', '11']
              },
              then: 'Junior'
            },
            {
              case: {
                $eq: ['$gradeLevel', '12']
              },
              then: 'Senior'
            }
          ],
          default: "Freshman"
        }
      }
    },
    $lookup: {
      from: 'RoadmapTasksCompleted',
      let: {
        username: '$username',
        gradeLevel: '$gradeLevel'
      },
      pipeline: [{
          $match: {
            monthToComplete: {
              $in: prevMonthsNames
            },
            $expr: {
              $and: [{
                  $eq: ['$username', '$$username']
                },
                {
                  $eq: ['$gradeLevel', '$$gradeLevel']
                }
              ]
            }
          }
        },
        {
          $count: 'count'
        }
      ],
      as: 'completedTasksCount'
    },
    $project: {
      username: '$username',
      email: '$email',
      phone: '$phone',
      fullName: '$fullName',
      completedTask: { $arrayElemAt: ['$completedTasksCount', 0] },
      status: {
        $let: {
          vars: {
            tasksCount: tasksCountMap['$gradeLevel'],
            completedTasksCount: '$completedTasksCount[0].count'
          },
          in: {
            $cond: {
              if: { $or: [
                { $eq: ['$$tasksCount', '$$completedTasksCount'] },
                { $lte: ['$$tasksCount', '$$completedTasksCount'] },
              ]},
              then: '$$tasksCount',
              else:'$$tasksCount'
            }
          }
        }
      }
    }
    $limit: 10,
    $skip: 10,
  }

Can you add a sample document to the post ? What is '$completedTasksCount[0].count ? — s7vr
– s7vr, Commented Aug 16, 2018 at 13:45

s7vr · Accepted Answer · 2018-08-16 14:28:04Z

1

You have to move the js map into the aggregation pipeline for you to be able to access the map.

I split $project stage into two and took the liberty to clean up the status calculation.

Something like

{"$project":{
  "username":"$username",
  "email":"$email",
  "phone":"$phone",
  "fullName":"$fullName",
  "completedTask":{"$arrayElemAt":["$completedTasksCount",0]},
  "tasksCountMap":[{"k":"Freshman","v":46},{"k":"Senior","v":10}]
}},
{"$addFields":{
  "status":{
    "$let":{
      "vars":{
        "tasksCount":{
          "$arrayElemAt":[
            "$tasksCountMap.v",
            {"$indexOfArray":["$tasksCountMap.k","$gradeLevel"]}
           ]
         },
        "completedTasksCount":"$completedTask.count"
      },
      "in":{
        "$cond":{
          "if":{"$lte":["$$tasksCount","$$completedTasksCount"]},
          "then":"$$tasksCount",
          "else":"$$completedTasksCount"
        }
      }
    }
  }
}}

answered Aug 16, 2018 at 14:28

s7vr

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4 Comments

izmaylovdev Over a year ago

tasksCount variable contain a valid value, thanks) but completedTasksCount is null...

izmaylovdev Over a year ago

also is null on project stage... if I remove all stages below lookup i get a valid value in results completedTasksCount:[{count: 27}] but if i even just add project stage: {"$project":{"completedTask": "$completedTasksCount"}}, i get completedTasksCount:[], and don't have completedTask in result... do you know why? Thanks for help.

s7vr Over a year ago

What framework do you use ? It looks like values are not passed from $lookup to next stage. Can you try the query in shell and verify ?

izmaylovdev Over a year ago

I created new question for this issue stackoverflow.com/questions/51881320/…

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