Remove all fields that are null

Question

How can I remove all fields that are null from all documents of a given collection?

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I have a collection of documents such as:

{
           


        

Answer 1

// run in mongo shell  

var coll = db.getCollection("collectionName");
var cursor = coll.find();
while (cursor.hasNext()) {
    var doc = cursor.next();
    var keys = {};
    var hasNull = false;
    for ( var x in doc) {
        if (x != "_id" && doc[x] == null) {
            keys[x] = 1;
            hasNull = true;
        }
    }
    if (hasNull) {
        coll.update({_id: doc._id}, {$unset:keys});
    }
}