go.cqrs中EventHandler的作用是什么
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EventHandler
type EventHandler interface { Handle(EventMessage) }
EventHandler定义了Handle方法
EventMessage
// EventMessage is the interface that a command must implement. type EventMessage interface { // AggregateID returns the ID of the Aggregate that the event relates to AggregateID() string // GetHeaders returns the key value collection of headers for the event. // // Headers are metadata about the event that do not form part of the // actual event but are still required to be persisted alongside the event. GetHeaders() map[string]interface{} // SetHeader sets the value of the header specified by the key SetHeader(string, interface{}) // Returns the actual event which is the payload of the event message. Event() interface{} // EventType returns a string descriptor of the command name EventType() string // Version returns the version of the event Version() *int }
EventMessage接口定义了AggregateID、GetHeaders、SetHeader、Event、EventType、Version方法
EventDescriptor
// EventDescriptor is an implementation of the event message interface. type EventDescriptor struct { id string event interface{} headers map[string]interface{} version *int } // NewEventMessage returns a new event descriptor func NewEventMessage(aggregateID string, event interface{}, version *int) *EventDescriptor { return &EventDescriptor{ id: aggregateID, event: event, headers: make(map[string]interface{}), version: version, } } // EventType returns the name of the event type as a string. func (c *EventDescriptor) EventType() string { return typeOf(c.event) } // AggregateID returns the ID of the Aggregate that the event relates to. func (c *EventDescriptor) AggregateID() string { return c.id } // GetHeaders returns the headers for the event. func (c *EventDescriptor) GetHeaders() map[string]interface{} { return c.headers } // SetHeader sets the value of the header specified by the key func (c *EventDescriptor) SetHeader(key string, value interface{}) { c.headers[key] = value } // Event the event payload of the event message func (c *EventDescriptor) Event() interface{} { return c.event } // Version returns the version of the event func (c *EventDescriptor) Version() *int { return c.version }
EventDescriptor定义了id、event、headers、version属性,它实现了EventMessage接口
PublishEvent
// PublishEvent publishes events to all registered event handlers func (b *InternalEventBus) PublishEvent(event EventMessage) { if handlers, ok := b.eventHandlers[event.EventType()]; ok { for handler := range handlers { handler.Handle(event) } } }
InternalEventBus的PublishEvent方法会遍历指定event.EventType()的handlers,挨个执行handler.Handle(event)方法
小结
go.cqrs的EventHandler定义了Handle方法;InternalEventBus的PublishEvent方法会遍历指定event.EventType()的handlers,挨个执行handler.Handle(event)方法。
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