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本文主要研究一下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介面定義了AggregateID、OriginalVersion、CurrentVersion、IncrementVersion、Apply、TrackChange、GetChanges、ClearChanges方法
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定義了id、version、changes屬性;AggregateID方法返回id;OriginalVersion方法返回version;CurrentVersion返回version+len(a。changes);IncrementVersion遞增version;TrackChange方法往changes增加event;GetChanges方法返回changes;ClearChanges會清空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介面定義了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 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定義了id、event、headers、version屬性;其EventType返回typeOf(c。event);AggregateID返回id;GetHeaders返回headers;SetHeader會設定header;Event方法返回event;Version返回version
小結
go。cqrs的AggregateRoot介面定義了AggregateID、OriginalVersion、CurrentVersion、IncrementVersion、Apply、TrackChange、GetChanges、ClearChanges方法。
doc
go。cqrs