Mongodb aggregation : how to merge two different groups

Question

Trying to get the count of various statuses & count of overdue items for each user. Below is the sample document:

[{
  _id:"12324332432",
  caseInd:"TASK123",
  TaskId:"12345",
  dueDate:ISODate("2021-03-22T00:00:00Z"),
  assingee:"ABC",
  status:"IN_PROGRESS",
  completionDate:null
},
{
  _id:"12324332433",
  caseInd:"TASK124",
  TaskId:"12345",
  dueDate:ISODate("2021-03-01T00:00:00Z"),
  assingee:"CDE",
  status:"IN_PROGRESS",
  completionDate:null
},
{
  _id:"12324332434",
  caseInd:"TASK125",
  TaskId:"12345",
  dueDate:ISODate("2021-03-31T00:00:00Z"),
  assingee:"ABC",
  status:"COMPLETED",
  completionDate:ISODate("2021-03-01T00:00:00Z")
}...]

Using aggregation, I want to get the count of tasks (completed,InProgress & overdue) for each user. like

[{
  _id : ABC , 
  data: [
      {status:"Completed", count:15},
      {status:"InProgress", count:3},
      {status:"Overdue", count:3}] 
  },{
  _id : CDE, 
  data: [
      {status:"Completed", count:5},
      {status:"InProgress", count:1},
      {status:"Overdue", count:0}] 
  }]

I have tired this solution, but not sure how to include overdue count.

db.colName.aggregate([ {$project: {_id:0, 
            dueDateIn:{$divide:[{$subtract:[new Date(),$dueDate]},86400000]},
            status:1,
            assignee:1
          }
    }, {
    $group:{
        _id:{"assignee":"$assignee", "status":"$status"},
        count:{$sum:1}
    },
    $group:{
        _id:"$_id.assignee" , result:{$push:{"status":"$_id.status", count:"$count"}}
    }
}]) ```

Any help would be highly appreciated. Thank you.

Answer 1

Take a look at the custom $accumulator in the $group pipeline.

After you group the documents with _id field, you can use the custom accumulator to count the status.

$group https://docs.mongodb.com/manual/reference/operator/aggregation/group/#pipe._S_group

$accumulator https://docs.mongodb.com/manual/reference/operator/aggregation/accumulator/#grp._S_accumulator