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Context

Interface

export interface ContextArgs<T> {
    dispatcher: Dispatcher;
    store: StoreLike<T>;
    options?: {
        strict?: boolean;
    };
}
export declare class Context<T> {
    constructor(args: ContextArgs<T>);
    readonly events: LifeCycleEventHub;
    getState(): StateMap<T>;
    onChange(handler: (changingStores: Array<StoreLike<any>>) => void): () => void;
    useCase(useCase: UseCaseFunction): UseCaseExecutor<FunctionalUseCase>;
    useCase<T extends UseCaseLike>(useCase: T): UseCaseExecutor<T>;
    transaction(name: string, transactionHandler: (transactionContext: TransactionContext) => Promise<any>): Promise<void>;
    onWillExecuteEachUseCase(handler: (payload: WillExecutedPayload, meta: DispatcherPayloadMeta) => void): () => void;
    onDispatch(handler: (payload: DispatchedPayload, meta: DispatcherPayloadMeta) => void): () => void;
    onDidExecuteEachUseCase(handler: (payload: DidExecutedPayload, meta: DispatcherPayloadMeta) => void): () => void;
    onCompleteEachUseCase(handler: (payload: CompletedPayload, meta: DispatcherPayloadMeta) => void): () => void;
    onErrorDispatch(handler: (payload: ErrorPayload, meta: DispatcherPayloadMeta) => void): () => void;
    release(): void;
}

Interface

export interface ContextArgs<T> {
    dispatcher: Dispatcher;
    store: StoreLike<T>;
    options?: {
        strict?: boolean;
    };

Context arguments

export declare class Context<T> {

Context class provide observing and communicating with Store and UseCase.

constructor(args: ContextArgs<T>);

dispatcher is an instance of Dispatcher. store is an instance of StoreLike implementation

Example

It is minimal initialization.

const context = new Context({
  dispatcher: new Dispatcher(),
  store: new MyStore()
});

In real case, you can pass StoreGroup instead of Store.

const storeGroup = new StoreGroup([
  new AStore(), new BStore(), new CStore()
]);
const context = new Context({
  dispatcher: new Dispatcher(),
  store: storeGroup
});

readonly events: LifeCycleEventHub;

Return almin life cycle events hub. You can observe life cycle events on almin.

See LifeCycleEventHub

getState(): StateMap<T>;

Return state value of StoreGroup or Store.

Example

If you pass StoreGroup to store of Constructor, Context#getState() return the state object that merge each stores's state.

const state = context.getState();
console.log(state);
// { aState, bState }

onChange(handler: (changingStores: Array<StoreLike<any>>) => void): () => void;

If anyone store that is passed to constructor is changed, handler is called. onChange arguments is an array of Store instances that are changed.

It returns unSubscribe function. If you want to release handler, the returned function.

It is useful for updating view in the handler.

Example

const unSubscribe = context.onChange(changingStores => {
  console.log(changingStores); // Array<Store>
  // Update view
});

Notes

If you want to know the change of registered store, please use context.onChange. context.onChange is optimized for updating View. By contrast, context.events.* is not optimized data. it is useful for logging.

Interface

useCase(useCase: UseCaseFunction): UseCaseExecutor<FunctionalUseCase>;
useCase<T extends UseCaseLike>(useCase: T): UseCaseExecutor<T>;

Context#useCase can accept two type of UseCase.

  • Instance of UseCase class
  • Functional UseCase

Example

// UseCase class pattern
class AwesomeUseCase extends UseCase {
   execute(...args){ }
}

context.useCase(new AwesomeUseCase()).execute([1, 2, 3]);

OR

// Functional UseCase pattern
const awesomeUseCase = ({dispatcher}) => {
   return (...args) => { }
};

context.useCase(awesomeUseCase).execute([1, 2, 3]);

transaction(name: string, transactionHandler: (transactionContext: TransactionContext) => Promise<any>): Promise<void>;

Transaction

  • Stability: Experimental
  • This feature is subject to change. It may change or be removed in future versions.

Create new Unit of Work and execute UseCase. You can prevent heavy updating of StoreGroup.

This feature only work in strict mode.

Difference with Context#useCase:

  • Do not update StoreGroup automatically
  • You should call transactionContext.commit() to update StoreGroup at any time

Example

context.transaction("A->B->C transaction", transactionContext => {
     return transactionContext.useCase(new ChangeAUseCase()).execute() // no update store
         .then(() => {
             return transactionContext.useCase(new ChangeBUseCase()).execute(); // no update store
         }).then(() => {
             return transactionContext.useCase(new ChangeCUseCase()).execute(); // no update store
         }).then(() => {
             transactionContext.commit(); // update store
             // replay: ChangeAUseCase -> ChangeBUseCase -> ChangeCUseCase
         });
 });

Notes

Transaction should be commit or exit

Transaction context should be called commit() or exit(). Because, this check logic avoid to silent failure of transaction.

And, transaction context should return a promise. In most case, transaction context should return transactionContext.useCase(useCase).execute().

Transaction disallow to do multiple commits

A transaction can do a single commit() Not to allow to do multiple commits in a transaction.

Use multiple transaction chain insteadof multiple commit in a transaction.

If you want to multiple commit, please file issue with the motivation.

Transaction is not lock system

The transaction does not lock updating of stores. The transaction method that create a new unit of work.

It means that the store may be updated by other unit of work during executing context.transaction. context.transaction provide the way for bulk updating.

A Unit of Work promise the order of events in the Unit of Work. But, This don't promise the order of events between Unit of Works.

 -----------------  commit   -----------------
| Unit of Work A |  ------> |                 |
 ----------------           |    StoreGroup   |
 -----------------  commit  |                 |
| Unit of Work B |  ------> |                 |
 ----------------            -----------------

Current implementation is READ COMMITTED of Transaction Isolation Levels.

No commit transaction get cancelled

You can write no commit() transaction. This transaction add commitment to the unit of work, but does not commit().

context.transaction("No commit transaction", transactionContext => {
     // No commit - Call `transactionContext.exit()` insteadof `transactionContext.commit()`
     return transactionContext.useCase(new LogUseCase()).execute().then(() => {
         transactionContext.exit();
     });
});

As a result, This transaction does not affect to Store. It means that Store can't received the payload of LogUseCase. Finally, that commitment get cancelled.

It is useful for logging UseCase. Logging UseCase does not need to update store/view. It only does log/send data to console/server.

TODO: rollback is not implemented

Rollback feature is generality implemented in the unit of work. We want to know actual use case of rollback before implementing this.

onWillExecuteEachUseCase(handler: (payload: WillExecutedPayload, meta: DispatcherPayloadMeta) => void): () => void;

Register handler function to Context. handler is called when each useCases will execute.

deprecated Use context.events.onWillExecuteEachUseCase insteadof it.

onDispatch(handler: (payload: DispatchedPayload, meta: DispatcherPayloadMeta) => void): () => void;

Register handler function to Context. handler is called the handler with user-defined payload object when the UseCase dispatch with payload. This onDispatch is not called at built-in event. It is filtered by Context. If you want to All dispatched event and use listen directly your dispatcher object. In other word, listen the dispatcher of new Context({dispatcher}).

Example

const dispatchUseCase = ({dispatcher}) => {
  return () => dispatcher.dispatch({ type: "fired-payload" });
};
context.onDispatch((payload, meta) => {
  console.log(payload); // { type: "fired-payload" }
});

context.useCase(dispatchUseCase).execute();

deprecated Use context.events.onDispatch insteadof it.

onDidExecuteEachUseCase(handler: (payload: DidExecutedPayload, meta: DispatcherPayloadMeta) => void): () => void;

handler is called when each useCases are executed.

deprecated Use context.events.onDidExecuteEachUseCase insteadof it.

onCompleteEachUseCase(handler: (payload: CompletedPayload, meta: DispatcherPayloadMeta) => void): () => void;

handler is called when each useCases are completed. This handler is always called asynchronously.

deprecated Use context.events.onCompleteEachUseCase insteadof it.

onErrorDispatch(handler: (payload: ErrorPayload, meta: DispatcherPayloadMeta) => void): () => void;

handler is called when some UseCase throw Error.

Throwing Error is following case:

  • Throw exception in a UseCase
  • Return rejected promise in a UseCase
  • Call UseCase#throwError(error)

deprecated Use context.events.onErrorDispatch insteadof it.

release(): void;

Release all events handler in Context. You can call this when no more call event handler