聊聊go.cqrs的Dispatcher

序

本文主要研究一下go.cqrs的Dispatcher

Dispatcher

type Dispatcher interface {
	Dispatch(CommandMessage) error
	RegisterHandler(CommandHandler, ...interface{}) error
}

Dispatcher接口定義了Dispatch、RegisterHandler方法

InMemoryDispatcher

type InMemoryDispatcher struct {
	handlers map[string]CommandHandler
}

//NewInMemoryDispatcher constructs a new in memory dispatcher
func NewInMemoryDispatcher() *InMemoryDispatcher {
	b := &InMemoryDispatcher{
		handlers: make(map[string]CommandHandler),
	}
	return b
}

//Dispatch passes the CommandMessage on to all registered command handlers.
func (b *InMemoryDispatcher) Dispatch(command CommandMessage) error {
	if handler, ok := b.handlers[command.CommandType()]; ok {
		return handler.Handle(command)
	}
	return fmt.Errorf("The command bus does not have a handler for commands of type: %s", command.CommandType())
}

//RegisterHandler registers a command handler for the command types specified by the
//variadic commands parameter.
func (b *InMemoryDispatcher) RegisterHandler(handler CommandHandler, commands ...interface{}) error {
	for _, command := range commands {
		typeName := typeOf(command)
		if _, ok := b.handlers[typeName]; ok {
			return fmt.Errorf("Duplicate command handler registration with command bus for command of type: %s", typeName)
		}
		b.handlers[typeName] = handler
	}
	return nil
}

InMemoryDispatcher定義了map[string]CommandHandler屬性，其Dispatch方法根據command.CommandType()獲取handler，然後執行handler.Handle(command)；其RegisterHandler方法遍歷commands，然後獲取command的type，挨個註冊到map[string]CommandHandler中

CommandHandler

// CommandHandler is the interface that all command handlers should implement.
type CommandHandler interface {
	Handle(CommandMessage) error
}

// CommandMessage is the interface that a command message must implement.
type CommandMessage interface {

	// AggregateID returns the ID of the Aggregate that the command relates to
	AggregateID() string

	// Headers returns the key value collection of headers for the command.
	Headers() map[string]interface{}

	// SetHeader sets the value of the header specified by the key
	SetHeader(string, interface{})

	// Command returns the actual command which is the payload of the command message.
	Command() interface{}

	// CommandType returns a string descriptor of the command name
	CommandType() string
}

CommandHandler接口定義了Handle方法；CommandMessage接口定義了AggregateID、Headers、SetHeader、Command、CommandType方法

小結

go.cqrs的Dispatcher接口定義了Dispatch、RegisterHandler方法；InMemoryDispatcher定義了map[string]CommandHandler屬性，其Dispatch方法根據command.CommandType()獲取handler，然後執行handler.Handle(command)；其RegisterHandler方法遍歷commands，然後獲取command的type，挨個註冊到map[string]CommandHandler中。

doc

• go.cqrs