Flutter - Create TypeAdapters in Hive

Flutter is open source framework from which we can create cross-platform applications with a single codebase. Hive is a local device storage that stores data in your phone storage. We store user profiles and tokens whether they are logged in or not like that thing. To deeply understand what hive please refer to this article Flutter – Store Data in Hive Local Database. In this article, we have covered almost all the data types but just missed 1 important data type i.e. TypeAdaptors we can understand this simply like models.

Step By Step Implementation

Let's learn how we can create a type adapter ( it will be automatically created) in Hive. We need to show how our model class will look like

Step 1: Create a New Project in Android Studio

To set up Flutter Development on Android Studio please refer to Android Studio Setup for Flutter Development, and then create a new project in Android Studio please refer to Creating a Simple Application in Flutter.

Step 2: Add the packages

We will add the following package in folder

dev_dependencies:
   hive_generator: ^1.1.2
   build_runner: ^2.1.8

Step 3: Create a sample model file

We will create a sample model file

Sample Json data:

{
    "userId": 1,
    "id": 1,
    "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
    "body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto"
}

Create a model file for this sample data:

import 'package:hive/hive.dart';

part 'post_models.g.dart';

@HiveType(typeId: 1)
class PostModel extends HiveObject {
  @HiveField(0)
  // Hivefield id  in brackets
  final  int id;
  @HiveField(1)
  final int userId;
  @HiveField(2)
  final String title;
  @HiveField(3)
  final String body;
  PostModel({
    required this.body,
    required this.id,
    required this.userId,
    required this.title,
  });
}

Important: During this creation you might get error on 3rd line but it will get remove after doing next steps

Step 4: Run the command to create a hive model class

Now we will run the command it will automatically create a model file named as post_models.g.dart its name is same as model class it will just create new file with .g in it.

flutter packages pub run build_runner build

To delete conflict during type adapters creation

flutter packages pub run build_runner build  --delete-conflicting-outputs

Step 5: Now we will register the type adapters in main function

We will register the type adapters like below

Future main() async {
  // It is used so that void main function can 
  // be intiated after successfully intialization of data
  WidgetsFlutterBinding.ensureInitialized();
  // To intialise the hive database
  await Hive.initFlutter();
  Hive.registerAdapter(PostModelAdapter());
  // Open Box for Post model
  await Hive.openBox<PostModelAdapter>("postBox");
  runApp(const MyApp());
}

Output:

Folder before type adaptors creation:

Folder after type adaptors creation:

Now you can access the box just like other box. In addition to that, do you know hive provide a lazy box also that means

var lazyBox = await Hive.openLazyBox('myLazyBox');

Let's understand what lazybox is? A lazy box is meant to reduce the amount of memory used by saving only the keys and not the contents of the box when it is opened. In this manner, Hive may obtain a value using the previously saved keys whenever a user requires it.