simple_persistence 0.3.4

A simple library for persisting data to disk.

Simple Persistence

A small package to easily store objects on disk.

Features

• Easily convert classes into storable classes
• No code-generation
• Multiple storage strategies for different applications
• No dependencies

Table of Contents

• Simple Persistence
  • Features
  • Table of Contents
  • Setup
    • Create a Storable class
    • Register deserializer for your Storable
      • Freezed
    • Create a Store for your Storable
    • Putting it together
  • Usage
    • KVStore

Setup

The setup is quite easy and requires three steps:

• Step 1: Create a Storable class
• Step 2: Register deserializer
• Step 3: Create a Store

Everything together

Create a Storable class

The first step is to make your class a Storable. You will need to implement the data getter and a function to create the object from a map (i.e. fromMap). In case you implement a copyWith method, make sure that you are copying the id field as well (as not make it be modifiable). This is important if you want to be able to update an object.

class User extends Storable {
    final String name;

    @override
    Map<String, dynamic> get data => {
        'name': name,
    };

    User.fromMap(Map<String, dynamic> map) : name = map['name'];
}

Now the User class is already done and prepared to be saved and loaded.

Register deserializer for your Storable

The next step is to register your class with the PersistenceManager singleton instance so it knows how to deserialize it:

PersistenceManager.I.register(User.fromMap);

After this, the StorableFactory.deserialize() function will be able to automatically figure out which class you want to deserialize if you give it the serialized data and return a User object.

Freezed

When the class of the object you are working with is not public, you can register the runtimeType instead:

@freezed
class User extends Storable with _$User {
    factory User.johnDoe() = _JohnDoeUser;

    // ...
}

// The actual type of the object returned from `User.johnDoe()` is hidden away in the
// code generated by freezed, so we use this workaround.
PersistenceManager.I.registerRuntimeType(
    instance: User.johnDoe(),
    deserializer: User.fromJson,
);

Create a Store for your Storable

The last step is to create a Store that is responsible for the read/write operations. Here you have choose between two different strategies: JsonFileStore will store all objects in one single file and BigJsonStore will have a separate file for every object (useful if you have a lot of data).

final userStore = JsonFileStore<User>(
    // This needs to be a path to a JSON file. It can be a [Future] as well. In Flutter it could e. g. be based on `getApplicationDocumentsDirectory()` from the path_provider package.
    path: '/.../.../test.json',
    // This needs to have the deseralizer for the correct type (in this case [User]) registered.
    storableFactory: sf,
);

And that's it. You can now use the operations on the store to persist your data.

Putting it together

All together a simple user.dart could look like this:

final sf = StorableFactory()
    ..registerDeserializer(User.fromMap);

class User extends Storable {
    static final store = JsonFileStore<User>(
        path: '/.../.../user.json',
        storableFactory: sf,
    );

    final String name;

    User(this.name);

    @override
    Map<String, dynamic> get data => {
        'name': name,
    };

    User.fromMap(Map<String, dynamic> map) : name = map['name'];

    User copyWith({String? name}) => 
        User(name ?? this.name)
            ..id = id; // copying the id is IMPORTANT, otherwise a new object will be created in the store.
}

Usage

After the example setup from above you can now easily persist and load data in your app:

void main() {
    var user = User('John Doe');

    // save user
    user = User.store.save(user); // the id will be set on the returned value

    // get user
    User.store.get(user.id);

    // update user
    final newUser = user.copyWith(name: 'Jane Doe');
    User.store.save(newUser);

    // get a stream of user updates
    // The stream will emit an update everytime the data for that id changes and will be
    // closed when the object is deleted.
    final stream = User.store.listen(user.id);

    // delete user
    User.store.delete(user.id);
}

KVStore

The [KVStore] class can be used to store simple key-value pairs. Each [KVStore] instance has a prefix that separates the key spaces.

void main() {
    // You need to initialize with a directory before creating any store
    KVStore.init('/.../.../');

    final kvs = KVStore('settings');

    // Usage

    // you can save any Type that can be automatically converted to JSON
    kvs.save('bool', true);
    kvs.save('int', 123);
    kvs.save('double', 123.45);
    kvs.save('string', 'the quick brown fox');
    kvs.save('list', [1, 2, 3]);

    kvs.get<int>('int'); // 123
    kvs.get<double>('int'); // 123.00

    kvs.delete('int');

    kvs.clear();
}