projector

Documentation

Index

• Variables
• type Error
  • func (e *Error) Cause() error
  • func (e *Error) Error() string
  • func (e *Error) Unwrap() error
• type EventHandler
  • func NewEventHandler(projector Projector, repo eh.ReadWriteRepo, options ...Option) *EventHandler
  • func (h *EventHandler) HandleEvent(ctx context.Context, event eh.Event) error
  • func (h *EventHandler) HandlerType() eh.EventHandlerType
  • func (h *EventHandler) SetEntityFactory(f func() eh.Entity)
• type Option
  • func WithEntityLookup(f func(eh.Event) uuid.UUID) Option
  • func WithIrregularVersioning() Option
  • func WithRetryOnce() Option
  • func WithWait() Option
• type Projector
• type Type
  • func (t Type) String() string

Variables

var (
	// ErrModelNotSet is when a model factory is not set on the EventHandler.
	ErrModelNotSet = errors.New("model not set")
	// ErrModelRemoved is when a model has been removed.
	ErrModelRemoved = errors.New("model removed")
	// Returned if the model has not incremented its version as predicted.
	ErrIncorrectProjectedEntityVersion = errors.New("incorrect projected entity version")
)

Types

type Error

type Error struct {
	// Err is the error that happened when projecting the event.
	Err error
	// Projector is the projector where the error happened.
	Projector string
	// Event is the event being projected.
	Event eh.Event
	// EntityID of related operation.
	EntityID uuid.UUID
	// EntityVersion is the version of the entity.
	EntityVersion int
}

Error is an error in the projector.

func (*Error) Cause

func (e *Error) Cause() error

Cause implements the github.com/pkg/errors Unwrap method.

func (*Error) Error

func (e *Error) Error() string

Error implements the Error method of the errors.Error interface.

func (*Error) Unwrap

func (e *Error) Unwrap() error

Unwrap implements the errors.Unwrap method.

type EventHandler

type EventHandler struct {
	// contains filtered or unexported fields
}

EventHandler is a CQRS projection handler to run a Projector implementation.

func NewEventHandler

func NewEventHandler(projector Projector, repo eh.ReadWriteRepo, options ...Option) *EventHandler

NewEventHandler creates a new EventHandler.

func (*EventHandler) HandleEvent

func (h *EventHandler) HandleEvent(ctx context.Context, event eh.Event) error

HandleEvent implements the HandleEvent method of the eventhorizon.EventHandler interface. It will try to find the correct version of the model, waiting for it the projector has the WithWait option set.

func (*EventHandler) HandlerType

func (h *EventHandler) HandlerType() eh.EventHandlerType

HandlerType implements the HandlerType method of the eventhorizon.EventHandler interface.

func (*EventHandler) SetEntityFactory

func (h *EventHandler) SetEntityFactory(f func() eh.Entity)

SetEntityFactory sets a factory function that creates concrete entity types.

type Option

type Option func(*EventHandler)

Option is an option setter used to configure creation.

func WithEntityLookup

func WithEntityLookup(f func(eh.Event) uuid.UUID) Option

WithEntityLookup can be used to provide an alternative ID (from the aggregate ID) for fetching the projected entity. The lookup func can for example extract another field from the event or use a static ID for some singleton-like projections.

func WithIrregularVersioning

func WithIrregularVersioning() Option

WithIrregularVersioning sets the option to allow gaps in the version numbers. This can be useful for projectors that project only some events of a larger aggregate, which will lead to gaps in the versions.

func WithRetryOnce

func WithRetryOnce() Option

WithRetryOnce adds a single retry in case of version mismatch. Useful to let racy projections finish witout an error.

func WithWait

func WithWait() Option

WithWait adds waiting for the correct version when projecting.

type Projector

type Projector interface {
	// ProjectorType returns the type of the projector.
	ProjectorType() Type

	// Project projects an event onto a model and returns the updated model or
	// an error.
	Project(context.Context, eh.Event, eh.Entity) (eh.Entity, error)
}

Projector is a projector of events onto models.

type Type

type Type string

Type is the type of a projector, used as its unique identifier.

func (Type) String

func (t Type) String() string

String returns the string representation of a projector type.