aggregate.go

// Copyright 2016 Jet Basrawi. All rights reserved.
//
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.

package ycq

//AggregateRoot is the interface that all aggregates should implement
type AggregateRoot interface {
	AggregateID() string
	OriginalVersion() int
	CurrentVersion() int
	IncrementVersion()
	Apply(events EventMessage, isNew bool)
	TrackChange(EventMessage)
	GetChanges() []EventMessage
	ClearChanges()
}

// 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 AggregateID
func (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{}
}