聊聊go.cqrs的DomainRepository

序

本文主要研究一下go.cqrs的DomainRepository

DomainRepository

// DomainRepository is the interface that all domain repositories should implement.
type DomainRepository interface {
    //Loads an aggregate of the given type and ID
    Load(aggregateTypeName string, aggregateID string) (AggregateRoot, error)

    //Saves the aggregate.
    Save(aggregate AggregateRoot, expectedVersion *int) error
}

DomainRepository定义了Load、Save方法

GetEventStoreCommonDomainRepo

// GetEventStoreCommonDomainRepo is an implementation of the DomainRepository
// that uses GetEventStore for persistence
type GetEventStoreCommonDomainRepo struct {
    eventStore         *goes.Client
    eventBus           EventBus
    streamNameDelegate StreamNamer
    aggregateFactory   AggregateFactory
    eventFactory       EventFactory
}

// Load will load all events from a stream and apply those events to an aggregate
// of the type specified.
//
// The aggregate type and id will be passed to the configured StreamNamer to
// get the stream name.
func (r *GetEventStoreCommonDomainRepo) Load(aggregateType, id string) (AggregateRoot, error) {

    if r.aggregateFactory == nil {
        return nil, fmt.Errorf("The common domain repository has no Aggregate Factory.")
    }

    if r.streamNameDelegate == nil {
        return nil, fmt.Errorf("The common domain repository has no stream name delegate.")
    }

    if r.eventFactory == nil {
        return nil, fmt.Errorf("The common domain has no Event Factory.")
    }

    aggregate := r.aggregateFactory.GetAggregate(aggregateType, id)
    if aggregate == nil {
        return nil, fmt.Errorf("The repository has no aggregate factory registered for aggregate type: %s", aggregateType)
    }

    streamName, err := r.streamNameDelegate.GetStreamName(aggregateType, id)
    if err != nil {
        return nil, err
    }

    stream := r.eventStore.NewStreamReader(streamName)
    for stream.Next() {
        switch err := stream.Err().(type) {
        case nil:
            break
        case *url.Error, *goes.ErrTemporarilyUnavailable:
            return nil, &ErrRepositoryUnavailable{}
        case *goes.ErrNoMoreEvents:
            return aggregate, nil
        case *goes.ErrUnauthorized:
            return nil, &ErrUnauthorized{}
        case *goes.ErrNotFound:
            return nil, &ErrAggregateNotFound{AggregateType: aggregateType, AggregateID: id}
        default:
            return nil, &ErrUnexpected{Err: err}
        }

        event := r.eventFactory.GetEvent(stream.EventResponse().Event.EventType)

        //TODO: No test for meta
        meta := make(map[string]string)
        stream.Scan(event, &meta)
        if stream.Err() != nil {
            return nil, stream.Err()
        }
        em := NewEventMessage(id, event, Int(stream.EventResponse().Event.EventNumber))
        for k, v := range meta {
            em.SetHeader(k, v)
        }
        aggregate.Apply(em, false)
        aggregate.IncrementVersion()
    }

    return aggregate, nil

}

// Save persists an aggregate
func (r *GetEventStoreCommonDomainRepo) Save(aggregate AggregateRoot, expectedVersion *int) error {

    if r.streamNameDelegate == nil {
        return fmt.Errorf("The common domain repository has no stream name delagate.")
    }

    resultEvents := aggregate.GetChanges()

    streamName, err := r.streamNameDelegate.GetStreamName(typeOf(aggregate), aggregate.AggregateID())
    if err != nil {
        return err
    }

    if len(resultEvents) > 0 {

        evs := make([]*goes.Event, len(resultEvents))

        for k, v := range resultEvents {
            //TODO: There is no test for this code
            v.SetHeader("AggregateID", aggregate.AggregateID())
            evs[k] = goes.NewEvent("", v.EventType(), v.Event(), v.GetHeaders())
        }

        streamWriter := r.eventStore.NewStreamWriter(streamName)
        err := streamWriter.Append(expectedVersion, evs...)
        switch e := err.(type) {
        case nil:
            break
        case *goes.ErrConcurrencyViolation:
            return &ErrConcurrencyViolation{Aggregate: aggregate, ExpectedVersion: expectedVersion, StreamName: streamName}
        case *goes.ErrUnauthorized:
            return &ErrUnauthorized{}
        case *goes.ErrTemporarilyUnavailable:
            return &ErrRepositoryUnavailable{}
        default:
            return &ErrUnexpected{Err: e}
        }
    }

    aggregate.ClearChanges()

    for k, v := range resultEvents {
        if expectedVersion == nil {
            r.eventBus.PublishEvent(v)
        } else {
            em := NewEventMessage(v.AggregateID(), v.Event(), Int(*expectedVersion+k+1))
            r.eventBus.PublishEvent(em)
        }
    }

    return nil
}

GetEventStoreCommonDomainRepo定义了eventStore、eventBus、streamNameDelegate、aggregateFactory、eventFactory属性，其Load方法先通过r.aggregateFactory.GetAggregate获取aggregate，再通过r.streamNameDelegate.GetStreamName(aggregateType, id)获取streamName，然后通过r.eventStore.NewStreamReader去遍历event，挨个执行aggregate.Apply(em, false)及aggregate.IncrementVersion()；其Save方法先通过aggregate.GetChanges()获取resultEvents，再遍历resultEvents构造goes.Event，之后通过streamWriter.Append写入，然后执行aggregate.ClearChanges()，最后执行r.eventBus.PublishEvent

小结

go.cqrs的DomainRepository定义了Load、Save方法；GetEventStoreCommonDomainRepo实现了DomainRepository接口，其Load方法主要是读取event，然后挨个执行aggregate.Apply；其Save方法主要是将aggregate.GetChanges()转换为event，然后通过streamWriter.Append写入，然后执行aggregate.ClearChanges()，最后执行r.eventBus.PublishEvent。

doc

• go.cqrs