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aggregate.go
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aggregate.go
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// Copyright (c) 2014 - Max Persson <max@looplab.se>
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package eventhorizon
// Aggregate is an interface representing a versioned data entity created from
// events. It receives commands and generates evens that are stored.
//
// The aggregate is created/loaded and saved by the Repository inside the
// Dispatcher. A domain specific aggregate can either imlement the full interface,
// or more commonly embed *AggregateBase to take care of the common methods.
type Aggregate interface {
// AggregateID returns the id of the aggregate.
AggregateID() UUID
// AggregateType returns the type name of the aggregate.
AggregateType() string
// Version returns the version of the aggregate.
Version() int
// IncrementVersion increments the aggregate version.
IncrementVersion()
// HandleCommand handles a command and stores events.
HandleCommand(Command) error
// ApplyEvent applies an event to the aggregate by setting its values.
ApplyEvent(events Event)
// StoreEvent stores an event until as uncommitted.
StoreEvent(Event)
// GetUncommittedEvents gets all uncommitted events for storing.
GetUncommittedEvents() []Event
// ClearUncommittedEvents clears all uncommitted events after storing.
ClearUncommittedEvents()
}
// AggregateBase is a CQRS aggregate base to embed in domain specific aggregates.
//
// A typical aggregate example:
// type UserAggregate struct {
// *eventhorizon.AggregateBase
//
// name string
// }
// The embedded aggregate is then initialized by the factory function in the
// callback repository.
type AggregateBase struct {
id UUID
version int
uncommittedEvents []Event
}
// NewAggregateBase creates an aggregate.
func NewAggregateBase(id UUID) *AggregateBase {
return &AggregateBase{
id: id,
uncommittedEvents: []Event{},
}
}
// AggregateID returns the ID of the aggregate.
func (a *AggregateBase) AggregateID() UUID {
return a.id
}
// Version returns the version of the aggregate.
func (a *AggregateBase) Version() int {
return a.version
}
// IncrementVersion increments the aggregate version.
func (a *AggregateBase) IncrementVersion() {
a.version++
}
// StoreEvent stores an event until as uncommitted.
func (a *AggregateBase) StoreEvent(event Event) {
a.uncommittedEvents = append(a.uncommittedEvents, event)
}
// GetUncommittedEvents gets all uncommitted events for storing.
func (a *AggregateBase) GetUncommittedEvents() []Event {
return a.uncommittedEvents
}
// ClearUncommittedEvents clears all uncommitted events after storing.
func (a *AggregateBase) ClearUncommittedEvents() {
a.uncommittedEvents = []Event{}
}