medartor

Description:

medartor

MeDARTor #
Simple, unambitious CQRS mediator implementation, .NET MediatR inspired.
// declares the message class (command/query) that is constructed with a username and returns a string
class GreetUserRequest implements IRequest<String> {
final String userName;

GreetUserRequest({
required this.userName,
});
}

// declare a class to handle the 'GreetUserRequest' message, which returns a string
class GreetUserHandler extends IRequestHandler<GreetUserRequest, String> {
@override
Future<String> handle(GreetUserRequest request) async {
return "Hello ${request.userName}!";
}
}

// Create a Mediator instance
final mediator = Medartor();

// Register the handler for the 'GreetUserRequest' message
mediator.register(GreetUserHandler());

// Create a 'GreetUserRequest' object
final request = GreetUserRequest(userName: "John");

// Send the message and get the response
final response = await mediator.send(request);

// print the answer
print(response); // print "Hello John!"
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Multiple handlers can also be used to attend to the same Request, for this case a Key associated with each handler must be registered to identify it and pass it as a parameter to the send method.
class HelloUserHandler extends IRequestHandler<GreetUserRequest, String> {
@override
Future<String> handle(GreetUserRequest request) async {
return "Hello ${request.userName}!";
}
}

class GoodbyeUserHandler extends IRequestHandler<GreetUserRequest, String> {
@override
Future<String> handle(GreetUserRequest request) async {
return "Goodbye ${request.userName}!";
}
}

// Create a Mediator instance
final mediator = Medartor();

// Register the handler for the 'GreetUserRequest' message with different keys
mediator.register(HelloUserHandler(), key: "helloHandler");
mediator.register(GoodbyeUserHandler(), key: "goodbyeHandler");

// Create a 'GreetUserRequest' object
final request = GreetUserRequest(userName: "John");

// Send the message and get the response
final response = await mediator.send(request, key: "helloHandler");
// print the answer
print(response); // print "Hello John!"

// Send the message and get the response
final response = await mediator.send(request, key: "goodbyeHandler");

// print the answer
print(response); // print "Goodbye John!"
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a good way to implement it in an architecture is to instantiate it and register its handlers at startup in a dependency injector.
The send function also supports a default handler function, which is executed in case the requested handler is not registered.
...
// Send the message and get the response
final response = await mediator.send(request, key: "goodbyeHandlerNotRegistered",
defaultHandler: (request) {
return Future.value('Hello default handler');
}
);

// print the answer
print(response); // print "Hello default handler"
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