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README
¶
eGo
eGo is a minimal library that help build event-sourcing and CQRS application through a simple interface, and it allows developers to describe their commands, events and states are defined using google protocol buffers. Under the hood, ego leverages Go-Akt to scale out and guarantee performant, reliable persistence.
Features
Domain Entity/Aggregate Root
The aggregate root is crucial for maintaining data consistency, especially in distributed systems. It defines how to handle the various commands (requests to perform actions) that are always directed at the aggregate root. In eGo commands sent the aggregate root are processed in order. When a command is processed, it may result in the generation of events, which are then stored in an event store. Every event persisted has a revision number and timestamp that can help track it. The aggregate root in eGo is responsible for defining how to handle events that are the result of command handlers. The end result of events handling is to build the new state of the aggregate root. When running in cluster mode, aggregate root are sharded.
- Commands handler: The command handlers define how to handle each incoming command, which validations must be applied, and finally, which events will be persisted if any. When there is no event to be persisted a nil can be returned as a no-op. Command handlers are the meat of the event sourced actor. They encode the business rules of your event sourced actor and act as a guardian of the Aggregate consistency. The command handler must first validate that the incoming command can be applied to the current model state. Any decision should be solely based on the data passed in the commands and the state of the Behavior. In case of successful validation, one or more events expressing the mutations are persisted. Once the events are persisted, they are applied to the state producing a new valid state.
- Events handler: The event handlers are used to mutate the state of the Aggregate by applying the events to it. Event handlers must be pure functions as they will be used when instantiating the Aggregate and replaying the event store.
To define an Aggregate Root, one needs to:
- the state of the aggregate root using google protocol buffers message
- the various commands that will be handled by the aggregate root
- the various events that are result of the command handlers and that will be handled by the aggregate root to return the new state of the aggregate root
- implements the
EntityBehavior[T State]interface where T is the generated golang struct of the prior defined aggregate root state.
Events Stream
Every event handled by Aggregate Root are pushed to an events stream. That enables real-time processing of events without having to interact with the events store
Projection
One can add a projection to the eGo engine to help build a read model. Projections in eGo rely on an offset store to track how far they have consumed events persisted by the write model. The offset used in eGo is a timestamp-based offset.
Events Store
One can implement a custom events store. See EventsStore. eGo comes packaged with two events store:
Offsets Store
One can implement a custom offsets store. See OffsetStore. eGo comes packaged with two offset store:
Cluster
The cluster mode heavily relies on Go-Akt clustering.
Examples
Check the examples
Installation
go get github.com/tochemey/ego
Sample
package main
import (
"context"
"errors"
"log"
"os"
"os/signal"
"syscall"
"github.com/google/uuid"
"github.com/tochemey/ego"
"github.com/tochemey/ego/eventstore/memory"
samplepb "github.com/tochemey/ego/example/pbs/sample/pb/v2"
"google.golang.org/protobuf/proto"
)
func main() {
// create the go context
ctx := context.Background()
// create the event store
eventStore := memory.NewEventsStore()
// create the ego engine
e := ego.NewEngine("Sample", eventStore)
// start ego engine
_ = e.Start(ctx)
// create a persistence id
entityID := uuid.NewString()
// create an entity behavior with a given id
behavior := NewAccountBehavior(entityID)
// create an entity
entity, _ := ego.NewEntity[*samplepb.Account](ctx, behavior, e)
// send some commands to the pid
var command proto.Message
// create an account
command = &samplepb.CreateAccount{
AccountId: entityID,
AccountBalance: 500.00,
}
// send the command to the entity. Please don't ignore the error in production grid code
account, _, _ := entity.SendCommand(ctx, command)
log.Printf("current balance: %v", account.GetAccountBalance())
// send another command to credit the balance
command = &samplepb.CreditAccount{
AccountId: entityID,
Balance: 250,
}
account, _, _ = entity.SendCommand(ctx, command)
log.Printf("current balance: %v", account.GetAccountBalance())
// capture ctrl+c
interruptSignal := make(chan os.Signal, 1)
signal.Notify(interruptSignal, os.Interrupt, syscall.SIGINT, syscall.SIGTERM)
<-interruptSignal
// stop the ego engine
_ = e.Stop(ctx)
os.Exit(0)
}
// AccountBehavior implements EntityBehavior
type AccountBehavior struct {
id string
}
// make sure that AccountBehavior is a true persistence behavior
var _ ego.EntityBehavior[*samplepb.Account] = &AccountBehavior{}
// NewAccountBehavior creates an instance of AccountBehavior
func NewAccountBehavior(id string) *AccountBehavior {
return &AccountBehavior{id: id}
}
// ID returns the id
func (a *AccountBehavior) ID() string {
return a.id
}
// InitialState returns the initial state
func (a *AccountBehavior) InitialState() *samplepb.Account {
return new(samplepb.Account)
}
// HandleCommand handles every command that is sent to the persistent behavior
func (a *AccountBehavior) HandleCommand(_ context.Context, command ego.Command, _ *samplepb.Account) (events []ego.Event, err error) {
switch cmd := command.(type) {
case *samplepb.CreateAccount:
// TODO in production grid app validate the command using the prior state
return []ego.Event{
&samplepb.AccountCreated{
AccountId: cmd.GetAccountId(),
AccountBalance: cmd.GetAccountBalance(),
},
}, nil
case *samplepb.CreditAccount:
// TODO in production grid app validate the command using the prior state
return []ego.Event{
&samplepb.AccountCredited{
AccountId: cmd.GetAccountId(),
AccountBalance: cmd.GetBalance(),
},
}, nil
default:
return nil, errors.New("unhandled command")
}
}
// HandleEvent handles every event emitted
func (a *AccountBehavior) HandleEvent(_ context.Context, event ego.Event, priorState *samplepb.Account) (state *samplepb.Account, err error) {
switch evt := event.(type) {
case *samplepb.AccountCreated:
return &samplepb.Account{
AccountId: evt.GetAccountId(),
AccountBalance: evt.GetAccountBalance(),
}, nil
case *samplepb.AccountCredited:
bal := priorState.GetAccountBalance() + evt.GetAccountBalance()
return &samplepb.Account{
AccountId: evt.GetAccountId(),
AccountBalance: bal,
}, nil
default:
return nil, errors.New("unhandled event")
}
}
Contribution
Contributions are welcome! The project adheres to Semantic Versioning and Conventional Commits. This repo uses Earthly.
There are two ways you can become a contributor:
- Request to become a collaborator, and then you can just open pull requests against the repository without forking it.
- Follow these steps
- Fork the repository
- Create a feature branch
- Set your docker credentials on your fork using the following secret names:
DOCKER_USERandDOCKER_PASS - Submit a pull request
Test & Linter
Prior to submitting a pull request, please run:
earthly +test
Documentation
¶
Index ¶
Constants ¶
This section is empty.
Variables ¶
var ( // ErrEngineRequired is returned when the eGo engine is not set ErrEngineRequired = errors.New("eGo engine is not defined") // ErrEngineNotStarted is returned when the eGo engine has not started ErrEngineNotStarted = errors.New("eGo engine has not started") // ErrUndefinedEntity is returned when sending a command to an undefined entity ErrUndefinedEntity = errors.New("eGo entity is not defined") )
Functions ¶
This section is empty.
Types ¶
type Engine ¶
type Engine struct {
// contains filtered or unexported fields
}
Engine represents the engine that empowers the various entities
func NewEngine ¶
func NewEngine(name string, eventsStore eventstore.EventsStore, opts ...Option) *Engine
NewEngine creates an instance of Engine
func (*Engine) AddProjection ¶
func (x *Engine) AddProjection(ctx context.Context, name string, handler projection.Handler, offsetStore offsetstore.OffsetStore, opts ...projection.Option) error
AddProjection add a projection to the running eGo engine and start it
func (*Engine) Subscribe ¶
func (x *Engine) Subscribe(ctx context.Context) (eventstream.Subscriber, error)
Subscribe creates an events subscriber
type Entity ¶
type Entity[T State] struct { // contains filtered or unexported fields }
Entity defines the event sourced persistent entity This handles commands in order
func NewEntity ¶
func NewEntity[T State](ctx context.Context, behavior EntityBehavior[T], engine *Engine) (*Entity[T], error)
NewEntity creates an instance of Entity
func (Entity[T]) SendCommand ¶
func (x Entity[T]) SendCommand(ctx context.Context, command Command) (resultingState T, revision uint64, err error)
SendCommand sends command to a given entity ref. This will return: 1. the resulting state after the command has been handled and the emitted event persisted 2. nil when there is no resulting state or no event persisted 3. an error in case of error
type EntityBehavior ¶
type EntityBehavior[T State] interface { // ID defines the id that will be used in the event journal. // This helps track the entity in the events store. ID() string // InitialState returns the event sourced actor initial state. // This is set as the initial state when there are no snapshots found the entity InitialState() T // HandleCommand helps handle commands received by the event sourced actor. The command handlers define how to handle each incoming command, // which validations must be applied, and finally, which events will be persisted if any. When there is no event to be persisted a nil can // be returned as a no-op. Command handlers are the meat of the event sourced actor. // They encode the business rules of your event sourced actor and act as a guardian of the event sourced actor consistency. // The command eventSourcedHandler must first validate that the incoming command can be applied to the current model state. // Any decision should be solely based on the data passed in the commands and the state of the Behavior. // In case of successful validation, one or more events expressing the mutations are persisted. // Once the events are persisted, they are applied to the state producing a new valid state. // Every event emitted are processed one after the other in the same order they were emitted to guarantee consistency. // It is at the discretion of the application developer to know in which order a given command should return the list of events // This is really powerful when a command needs to return two events. For instance, an OpenAccount command can result in two events: one is AccountOpened and the second is AccountCredited HandleCommand(ctx context.Context, command Command, priorState T) (events []Event, err error) // HandleEvent handle events emitted by the command handlers. The event handlers are used to mutate the state of the event sourced actor by applying the events to it. // Event handlers must be pure functions as they will be used when instantiating the event sourced actor and replaying the event journal. HandleEvent(ctx context.Context, event Event, priorState T) (state T, err error) }
EntityBehavior defines an event sourced behavior when modeling a CQRS EntityBehavior.
type Option ¶
type Option interface {
// Apply sets the Option value of a config.
Apply(e *Engine)
}
Option is the interface that applies a configuration option.
func WithCluster ¶
func WithCluster(provider discovery.Provider, partitionCount uint64, minimumPeersQuorum uint16, host string, remotingPort, gossipPort, peersPort int) Option
WithCluster enables cluster mode
func WithTelemetry ¶
WithTelemetry sets the telemetry engine
Source Files
Directories