pymongo (v. 4.3.3) No array filter found for identifier 'elem' in path 'grades.$[elem]

Question

I am getting consistent error: No array filter found for identifier 'elem' in path 'grades.$[elem] for sample code in Mongo Document: https://www.mongodb.com/docs/manual/reference/operator/update/positional-filtered/

db.students.insert_many( [
   {
      "_id" : 1,
      "grades" : [
         { "grade" : 80, "mean" : 75, "std" : 6 },
         { "grade" : 85, "mean" : 100, "std" : 4 },
         { "grade" : 85, "mean" : 100, "std" : 6 }
      ]
   },
   {
      "_id" : 2,
      "grades" : [
         { "grade" : 90, "mean" : 100, "std" : 6 },
         { "grade" : 87, "mean" : 100, "std" : 3 },
         { "grade" : 85, "mean" : 100, "std" : 4 }
      ]
   }
] )

and the query:

cursor = db.students.update_many(
    filter={ },
    update={
        '$inc'        : {"grades.$[elem].std": -1},
        'arrayFilters': [{"elem.grade": {'$gte': 80}, "elem.std": {'$gt': 5}}],
    },
    upsert=True
)

and the consistent error I get: pymongo.errors.WriteError: No array filter found for identifier 'elem' in path 'grades.$[elem].std'

Answer 1

the corect query need to look as follow:

db.students.update_many(
 {},
 {"$inc" : {"grades.$[elem].std" : -1}}, 
 array_filters=[{"elem.grade":{"$gte" : 80 }, "elem.std":{"$lte" :5} }]
)

Explained: Considering usual update query consist of 3x sections:

1. filter matching query section
2. update section
3. options section

The correct position of array_filters is not inside the update section , but afterwards in the options section.

mongo playgraund