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本文次要钻研一下go.cqrs的AggregateRoot
AggregateRoot
//AggregateRoot is the interface that all aggregates should implementtype AggregateRoot interface { AggregateID() string OriginalVersion() int CurrentVersion() int IncrementVersion() Apply(events EventMessage, isNew bool) TrackChange(EventMessage) GetChanges() []EventMessage ClearChanges()}AggregateRoot接口定义了AggregateID、OriginalVersion、CurrentVersion、IncrementVersion、Apply、TrackChange、GetChanges、ClearChanges办法
AggregateBase
// AggregateBase is a type that can be embedded in an AggregateRoot// implementation to handle common aggragate behaviour//// All required methods to implement an aggregate are here, to implement the// Aggregate root interface your aggregate will need to implement the Apply// method that will contain behaviour specific to your aggregate.type AggregateBase struct { id string version int changes []EventMessage}// NewAggregateBase contructs a new AggregateBase.func NewAggregateBase(id string) *AggregateBase { return &AggregateBase{ id: id, changes: []EventMessage{}, version: -1, }}// AggregateID returns the AggregateIDfunc (a *AggregateBase) AggregateID() string { return a.id}// OriginalVersion returns the version of the aggregate as it was when it was// instantiated or loaded from the repository.//// Importantly an aggregate with one event applied will be at version 0// this allows the aggregates to match the version in the eventstore where// the first event will be version 0.func (a *AggregateBase) OriginalVersion() int { return a.version}// CurrentVersion returns the version of the aggregate as it was when it was// instantiated or loaded from the repository.//// Importantly an aggregate with one event applied will be at version 0// this allows the aggregates to match the version in the eventstore where// the first event will be version 0.func (a *AggregateBase) CurrentVersion() int { return a.version + len(a.changes)}// IncrementVersion increments the aggregate version number by one.func (a *AggregateBase) IncrementVersion() { a.version++}// TrackChange stores the EventMessage in the changes collection.//// Changes are new, unpersisted events that have been applied to the aggregate.func (a *AggregateBase) TrackChange(event EventMessage) { a.changes = append(a.changes, event)}// GetChanges returns the collection of new unpersisted events that have// been applied to the aggregate.func (a *AggregateBase) GetChanges() []EventMessage { return a.changes}//ClearChanges removes all unpersisted events from the aggregate.func (a *AggregateBase) ClearChanges() { a.changes = []EventMessage{}}AggregateBase定义了id、version、changes属性；AggregateID办法返回id；OriginalVersion办法返回version；CurrentVersion返回version+len(a.changes)；IncrementVersion递增version；TrackChange办法往changes减少event；GetChanges办法返回changes；ClearChanges会清空changes
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办法
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 descriptorfunc 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 keyfunc (c *EventDescriptor) SetHeader(key string, value interface{}) { c.headers[key] = value}// Event the event payload of the event messagefunc (c *EventDescriptor) Event() interface{} { return c.event}// Version returns the version of the eventfunc (c *EventDescriptor) Version() *int { return c.version}EventDescriptor定义了id、event、headers、version属性；其EventType返回typeOf(c.event)；AggregateID返回id；GetHeaders返回headers；SetHeader会设置header；Event办法返回event；Version返回version
小结
go.cqrs的AggregateRoot接口定义了AggregateID、OriginalVersion、CurrentVersion、IncrementVersion、Apply、TrackChange、GetChanges、ClearChanges办法。
doc
- go.cqrs