Redarx

Experimental Dart State Management humbly inspired by ngrx <= Redux <= Elm, André Stalz work & Parsley.

Examples

• Redarx with AngularDart example
• Redarx with Vanilla Dart example

Principles

Requests to Commands Mapping via CommanderConfig

final requestMap = new Map<RequestType, CommandBuilder>()
  ..[RequestType.ADD_TODO] = AddTodoCommand.constructor()
  ..[RequestType.ARCHIVE] = ArchiveCommand.constructor()
  ..[RequestType.UPDATE_TODO] = UpdateTodoCommand.constructor()
  ..[RequestType.CLEAR_ARCHIVES] = ClearArchivesCommand.constructor()
  ..[RequestType.TOGGLE_SHOW_COMPLETED] = ToggleShowArchivesCommand.constructor();

Initialization

final cfg = new CommanderConfig<RequestType>(requestMap);
final store = new Store<TodoModel>(() => new TodoModel.empty());
final dispatcher = new Dispatcher();

final cmder = new Commander(cfg, store, dispatcher.onRequest);

var app = new AppComponent(querySelector('#app') )
..model$ = store.data$
..dispatch = dispatcher.dispatch
..render();

Dispatching requests

RequestType are defined via an enum

enum RequestType {
  ADD_TODO,
  UPDATE_TODO,
  ARCHIVE,
  CLEAR_ARCHIVES,
  TOGGLE_SHOW_COMPLETED
}

Requests are defined by a type and an optional payload.

dispatch( new Request(
    RequestType.ADD_TODO, withData: new Todo(fldTodo.value))
    );

Commands

Requests are mapped to commands by Commander and passed to the store.update()

exec(Request a) {
    store.update(config[a.type](a.payload));
  }

The commands define a public exec method which receive the currentState and return the new one.

class AddTodoCommand extends Command<TodoModel> {
  Todo todo;

  AddTodoCommand(this.todo);

  @override
  TodoModel exec(TodoModel model) => model..items.add(todo);

  static CommandBuilder constructor() {
    return (Todo todo) => new AddTodoCommand(todo);
  }
}

Async Commands

Async commands allows async evaluation of the new state

Store

Basically a (stream<Command<Model>>) => stream<Model> transformer

Receives new commands, and executes those with the current state/Model

Use a CommandStreamReducer<S extends Command, T extends AbstractModel> to stream reduced states

The store manage a stream of immutable states instances.

Reversible Store

The reversible store keep a history list of all executed commands and allow cancelling.

it provide an access to currentState by reducing all the commands history.

State listening

The store exposes a stream of immutable states

Stream<TodoModel> _model$;

set model$(Stream<TodoModel> value) {
_model$ = value;
    
modelSub = _model$.listen((TodoModel model) {
      list.todos = model.todos;
      footer.numCompleted = model.numCompleted;
      footer.numRemaining = model.numRemaining;
      footer.showCompleted = model.showCompleted;
    });
  }

Experimental multi-channel dispatcher (0.6.0)

Async commands are maybe not the best way to connect a Firebase data-source.

The redarx-ng-firebase example shows a way to dispatch firebase queries via a new dispatcher method : query.

Queries are dispatched to a Firebase service, which update the base. The service handles firebase.database child and values events and dispatch update request via the dispatch() method.

Event$ » Request$ » Command$ » state$

The Application State is managed in a Store.

State is updated by commands, and the store keep a list of executed commands.

State is evaluated by commands updates,

In reversible-store, cancellation is allowed by simply remove the last command from "history".

A Commander listen to a stream of Requests dispatched by a Dispatcher injected in the application components | controllers | PM | VM

Each Request is defined by an RequestType enum, and can contains data.

Requests are "converted" to commands by the Commander, based on the CommanderConfig.map definition

• the dispatcher.dispatch function is injected in view || controller || PresentationModel || ViewModel

• Request are categorized by types, types are defined in RequestType enum

• the dispatcher stream Requests

• the dispatcher requestStream is injected in Commander, the commander listen to it,transforms Request to Command and transfer to the store.apply( command ) method

• each Request is tied to a command via a CommanderConfig which is injected in Commander

// instanciate commands form requests 
config[request.type](request.payload);

• Commander need a CommanderConfig containing a Map<RequestType,CommandBuilder>
• the store then execute commandHistory and push the new model value to a model stream

TODO

• ~~fix the generic/command ( mess)~~
• ~~implements a Scan stream transformer » to allow only run the last commands & emit the last reduced state~~
• ~~async commands~~
• ~~test Angular integration~~
• ~~test with Firebase~~
• use values types cf built_value
• time travel / history UI
• typed Request ? BookRequest, UserRequest ...?
• tests
• external config file ?
• ...

Doubts

• use a EnumClass implementation rather than dart enum type
• dispatcher : use a streamController.add rather than dispatch method ?
• multiple store ? dispatcher ? commander ?
• each component could set an Request stream and the commander could maybe listen to it

Goals

• study Dart : streams, generics, annotations, asynchrony...
• study Redux & ngrx, play with reducers & Request/Commands mapping...
• and more studies, more experiments, more play...
• define a solid architecture for my coming projects