count total number of elements inside an array in document - MongoDB

Question

I have a document related to the role or designations of employees. This is the document structure.

{
    \"_id\" : ObjectId(\"5660c2a5b6fcba2d47baa2d9\"),
          


        

Answer 1

You have to use $group instead:

db.employee_role.aggregate(
   {
        $group: {
            _id: "$role_title",
            total: { $sum: { $size:"$employees" } }
        }
   }
)

You group by role_title and then, you add the number of employees.

Answer 2

You could use this:

db.employee_role.aggregate(
  [
    {
      $match: { role_title: "Carpenter" }
    },
    {
      $group: {
        _id: "$role_title",
        total: { $sum: { $size: "$employees"} }
      }
    }
  ]
)