How to get all result if unwind field does not exist in mongodb

Question

i am trying to fetch data from collection form below query:

     db.getCollection('jobs').aggregate(
    {$match :{"slug":"bath-room-designer-for-whole-floor-772000"}},
    {$unwind: "$job_activity"},
    {$lookup: {
            "from":"users",
            "localField":"job_activity.user_id",
            "foreignField":"_id",
            "as": "user_details"
        }
    },
    {$unwind: { path: "$user_details", preserveNullAndEmptyArrays: false } },
    {$group: {
                "_id": "$_id", 
                "Job_detail": {"$push": "$job_activity"},
                "job_activity": {"$push": "$job_activity"},
                "user_details": {"$push": "$user_details"}
            }
    }
    
)

But it result empty data wherever datat exists in the collection for the $match but job_activity is not exist for this slug

can anyone help Thanks

Answer 1

use the preserveNullAndEmptyArrays of $unwind to keep documents where job_activity doesn't exist or is empty

so use this $unwind stage:

{
  $unwind:
    {
      path: "$job_activity",
      preserveNullAndEmptyArrays: true
    }
}