group in mongo excluding null values

Question

I have mongo query which does the group operation on the documents.

I have almost got the expected results except that I want to refine the results without empty or

Answer 1

You need an extra $match pipeline step that will filter the incoming documents based on the embedded field "$productAttribute.colour" existing and not null:

    db.productMetadata.aggregate([
    { 
        "$match": {
            "productAttribute.colour": { 
                "$exists": true, 
                "$ne": null 
            }
        }    
    },
    { 
        "$group": {
            "_id": {
                "color": "$productAttribute.colour",
                "gender": "$productAttribute.gender"
            },
            "count": { 
                "$sum": 1 
            }
        }   
    }        
]);