how to remove a subset of a mongodb collection that only has certain fields.

dropfew.js

db.collection.find({"changes.objectSid": { $exists: 1}, "changes.pwdLastSet": { $exists: 1 }}).forEach(function(doc) {                                                                                                                                
    var other_found = false;                                                                                                                                                                                                                  
                                                                                                                                                                                                                                              
    for (key in doc.changes) {                                                                                                                                                                                                                
        if (key != 'objectSid' && key != 'pwdLastSet') {                                                                                                                                                                                      
            other_found = true;                                                                                                                                                                                                               
            break;                                                                                                                                                                                                                            
        }                                                                                                                                                                                                                                     
    }                                                                                                                                                                                                                                         
                                                                                                                                                                                                                                              
    if (!other_found) {                                                                                                                                                                                                                       
        printjson(doc);                                                                                                                                                                                                                       
        db.collection.remove(doc);                                                                                                                                                                                                                    
    }                                                                                                                                                                                                                                         
});