关于golang:聊聊gocqrs的DomainRepository

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本文次要钻研一下 go.cqrs 的 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 办法

// 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 办法先通过 r.aggregateFactory.GetAggregate 获取 aggregate，再通过 r.streamNameDelegate.GetStreamName(aggregateType, id) 获取 streamName，而后通过 r.eventStore.NewStreamReader 去遍历 event，挨个执行 aggregate.Apply(em, false) 及 aggregate.IncrementVersion()；其 Save 办法先通过 aggregate.GetChanges() 获取 resultEvents，再遍历 resultEvents 结构 goes.Event，之后通过 streamWriter.Append 写入，而后执行 aggregate.ClearChanges()，最初执行 r.eventBus.PublishEvent

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