anchor.diff:        'comments': [{'user_id': users['jdoe']["_id"], 'body': "great article!"}]
       }
     ]);
  -  print(
  -      "===================================================================================");
  +  print("====================================================================");
     print(">> Articles ordered by title ascending");
     await articlesCollection.find(where.sortBy('title')).forEach((article) {
       print(
  -        "[${article['title']}]:[${article['body']}]:[author_id: ${article['author_id']}]");
  +        "[${article['title']}]:[${article['body']}]:[${article['author_id'].toHexString()}]");
     });
     await db.close();
   }
  
positive.code:     },
      {'name': 'Jorge Luis Borges', 'email': 'jorge@borges.com', 'age': 123}
    ]);
    await collection.find().forEach((v) {
      authors[v["name"]] = v;
    });
    print(
        "===================================================================================");
    print(">> Authors ordered by age ascending");
    await db.ensureIndex('authors', key: 'age');
    await collection.find(where.sortBy('age')).forEach(
        (auth) => print("[${auth['name']}]:[${auth['email']}]:[${auth['age']}]"));
    print(
        "===================================================================================");
    print(">> Adding Users");
    usersCollection = db.collection("users");
    await usersCollection.insertAll([
      {'login': 'jdoe', 'name': 'John Doe', 'email': 'john@doe.com'},
      {'login': 'lsmith', 'name': 'Lucy Smith', 'email': 'lucy@smith.com'}
    ]);
    await db.ensureIndex('users', keys: {'login': -1});
    await usersCollection.find().forEach((user) => users[user["login"]] = user);
    print(
        "===================================================================================");
    print(">> Users ordered by login descending");
    await usersCollection.find(where.sortBy('login', descending: true)).forEach(
        (user) =>
            print("[${user['login']}]:[${user['name']}]:[${user['email']}]"));
    print(
        "===================================================================================");
    print(">> Adding articles");
    articlesCollection = db.collection("articles");
    await articlesCollection.insertAll([
      {
        'title': 'Caminando por Buenos Aires',
  
negative.code: import 'package:mongo_dart/mongo_dart.dart';
  import 'dart:io' show Platform;
  
  var host = Platform.environment['MONGO_DART_DRIVER_HOST'] ?? '127.0.0.1';
  var port = Platform.environment['MONGO_DART_DRIVER_PORT'] ?? '27017';
  
  main() async {
    Db db = new Db("mongodb://$host:$port/mongo_dart-blog");
    Map<String, Map> authors = new Map<String, Map>();
    Map<String, Map> users = new Map<String, Map>();
    await db.open();
    await db.drop();
    print("====================================================================");
    print(">> Adding Authors");
    var collection = db.collection('authors');
    await collection.insertAll([
      {
        'name': 'William Shakespeare',
  