sequence

This paper mainly studies the Dispatcher of GO. CQRS

Dispatcher

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

The Dispatcher interface defines the Dispatch and RegisterHandler methods

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 }Copy the code

InMemoryDispatcher defines the Map [String]CommandHandler property, whose Dispatch method retrieves a handler from command.mandType (). Then execute handler.Handle(command); The RegisterHandler method iterates through commands and retrieves the command type, registering it one by one with a Map [String]CommandHandler

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 }Copy the code

The CommandHandler interface defines the Handle method; The CommandMessage interface defines the AggregateID, Headers, SetHeader, Command, and CommandType methods

summary

The Dispatcher interface of GO. CQRS defines Dispatch and RegisterHandler methods. InMemoryDispatcher defines the Map [String]CommandHandler property, whose Dispatch method retrieves a handler from command.mandType (). Then execute handler.Handle(command); The RegisterHandler method iterates through commands and retrieves the command type, registering it one by one with a Map [String]CommandHandler.

doc

  • go.cqrs