How to save deletion in a deeply nested MongoDB document

I am new to MongoDB and I am using MongoDB shell to perform the operations. I am working to remove the array named Process from all the Items, but it seems that I do not grasp the remove concept correctly. The documents we use are deeply nested - we do not know how many items there are, or how deep the level of nesting.
What I tried so far is to use recursion to iterate through the items:



    function removeAllProcessFields(docItems)
    {
        if(Array.isArray(docItems))
        {
            docItems.forEach(function(item)
                {
                   print("idItem: "+item._id);
                   if(item.Process == null)
                   {
                      print("Process null");
                   }
                   else
                   {
                      $unset: { Process: ""}
                   }
                   removeAllProcessFields(item.Items);
            })
        }
    }
    
    var docs = db.getCollection('MyCollection').find({})
    docs.forEach(function(doc)
    {
        print("idDoc: "+doc._id);
        removeAllProcessFields(doc.Items);
    })

But I have difficulties on using unset properly to save the operation.
An example document would be:



    {
        "_id": "622226d319517e83e8ed6151",
        "Name": "test1",
        "Description": "",
        "Items": [{
            "_id": "622226d319517e83e8ed614e",
            "Name": "test-item",
            "Description": "",
            "Process": [{
                "Name": "Step1"
            }, {
                "Name": "Step2"
            }],
            "Items": [{
                    "_id": "622226d319517e83e8ed614f",
                    "Name": "test-subItem1",
                    "Description": "",
                    "Process": [{
                        "Name": "StepSub1"
                    }, {
                        "Name": "StepSub2"
                    }, {
                        "Name": "StepSub3"
                    }],
                    "Items": []
                },
                {
                    "_id": "622226d319517e83e8ed6150",
                    "Name": "test-subItem2",
                    "Description": "",
                    "Process": [{
                        "Name": "StepSub4"
                    }, {
                        "Name": "StepSub5"
                    }, {
                        "Name": "StepSub6"
                    }],
                    "Items": []
                }
    
            ]
        }]
    }

What I hope to achieve would be:



    {
        "_id": "622226d319517e83e8ed6151",
        "Name": "test1",
        "Description": "",
        "Items": [{
            "_id": "622226d319517e83e8ed614e",
            "Name": "test-item",
            "Description": "",
            "Items": [{
                    "_id": "622226d319517e83e8ed614f",
                    "Name": "test-subItem1",
                    "Description": "",
                    "Items": []
                },
                {
                    "_id": "622226d319517e83e8ed6150",
                    "Name": "test-subItem2",
                    "Description": "",
                    "Items": []
                }
    
            ]
        }]
    }

Solution

Something like this maybe using the $[] positional operator:

db.collection.update({},
{
 $unset: {
  "Items.$[].Items.$[].Process": 1,
  "Items.$[].Process": 1
}
})

You just need to construct it in the recursion ...

playground

JavaScript recursive function example:

 mongos> db.rec.find()
{ "_id" : ObjectId("622a6c46ae295edb276df8e2"), "Items" : [ { "a" : 1 }, { "Items" : [ { "Items" : [ { "Items" : [ ], "Process" : [ 1, 2, 3 ] } ], "Process" : [ 4, 5, 6 ] } ], "Process" : [ ] } ] }

 mongos> db.rec.find().forEach(function(obj){ var id=obj._id,ar=[],z=""; function x(obj){ if(typeof obj.Items != "undefined" ){ obj.Items.forEach(function(k){ if( typeof k.Process !="undefined" ){ z=z+".Items.$[]";ar.push(z.substring(1)+".Process") }; if(typeof k.Items != "undefined"){x(k)}else{}  }) }else{}  };x(obj);ar.forEach(function(del){print( "db.collection.update({_id:ObjectId('"+id+"')},{$unset:{'"+del+"':1}})" );}) })

 db.collection.update({_id:ObjectId('622a6c46ae295edb276df8e2')},{$unset:{'Items.$[].Process':1}})
 db.collection.update({_id:ObjectId('622a6c46ae295edb276df8e2')},{$unset:{'Items.$[].Items.$[].Process':1}})
 db.collection.update({_id:ObjectId('622a6c46ae295edb276df8e2')},{$unset:{'Items.$[].Items.$[].Items.$[].Process':1}})
 mongos>

Explained:

Loop over all documents in collection with forEach
Define recursive function x that will loop over any number of nested Items and identify if there is Process field and push to array ar
Finally loop over array ar and construct the update $unset query , in the example only printed for safety , but you can improve generating single query per document and executing unset query ...