最后更新于2023年3月1日 10:23:13
参考的这个文章:https://martinfowler.com/eaaDev/EventSourcing.html
用C sharp实现的,我改写成Golang了
最简单的例子
func main() {eProc := NewEventProcessor()//refact := Cargo{Name: "Refactoring"}kr := &Ship{Name: "King Roy"}sfo := &Port{Name: "San Francisco", Country: "US"}//la := Port{Name: "Los Angeles", Country: "US"}//yyv := Port{Name: "Vancouver", Country: "Canada"}// Test 1ev := ArrivalEvent{DomainEvent: DomainEvent{Recorded: time.Now(),Occurred: time.Date(2005, time.November, 1, 0, 0, 0, 0, time.Local),},Port: sfo,Ship: kr,}eProc.Process(&ev)jiayulog.Logger.DebugP(sfo)jiayulog.Logger.DebugP(kr.Port)pretty.Log(eProc)
}
这里面的jiayulog是我自己搞了一个log,pretty-print结构体,用fmt.Print来代替就行。
首先main函数,定义了一艘船"King Roy"号,还有几个港口,这个例子里面就用了一个旧金山。
定义了一个到达事件,大概就是King Roy号在2005年到达了旧金山港口,这件事记录于time.Now()这个时刻。
把这个事情扔进事件处理器EventProcessor里面处理一下(更新Ship, Port等实体、记录日志)
// EventLog
type EventLog struct {ls []EventBase
}func (i *EventLog) Add(e EventBase) {i.ls = append(i.ls, e)
}// EventProcessor
type EventProcessor struct {log EventLog
}func NewEventProcessor() *EventProcessor {return &EventProcessor{log: EventLog{ls: make([]EventBase, 0)},}
}func (i *EventProcessor) Process(e EventBase) {e.Process()i.log.Add(e)
}
上面这个是事件处理器+事件日志,eventProcessor.Process方法里,首先让传进来的event调用自己的process方法,然后添加日志;
事件日志很简单,就是一个切片,一直往里面append就可以了,这个可以持久化到数据库里面。
// ArrivalEvent
type ArrivalEvent struct {DomainEventPort *PortShip *Ship
}func (i *ArrivalEvent) Process() {i.Ship.HandleArrival(*i)
}// DepartureEvent
type DepartureEvent struct {DomainEventPort *PortShip *Ship
}func (i *DepartureEvent) Process() {i.Ship.HandleDeparture(*i)
}// DomainEvent
type DomainEvent struct {Recorded time.TimeOccurred time.Time
}type EventBase interface {Process()
}
然后是实现了一个EventBase接口,下面有两种不同的event,到达event+出发event。在各自的Process方法里面调用Ship的处理方法,这里把整个event当做参数传进handle*方法里面i.Ship.HandleDeparture(*i)
,就很怪,不知道这样写好不好……
var PortAtSea = &Port{Name: "AT_SEA",Country: "N/A",
}// Entities
type Ship struct {Name stringPort *PortCargos []Cargo
}func (i *Ship) HandleArrival(ev ArrivalEvent) {i.Port = ev.Portfor _, c := range i.Cargos {c.HandleArrival(ev)}
}func (i *Ship) HandleDeparture(ev DepartureEvent) {i.Port = PortAtSea
}type Port struct {Name stringCountry string
}// Cargo
type Cargo struct {Name string
}
再接着是一些实体类,船、港口、货物。需要注意的是船出发了它就在海上了,port这里就用一个PortAtSea表示没有停靠任何港口。
注意!!!HandleArrivel和HandleDeparture相当于把一个event传递进实体里面了!!!这是设计的思路!!!学吧老哥!!!
深入一点:我们的货物是否经过了加拿大
加拿大是tm挺危险,俺们那边老有人一不小心就自驾到温莎了,毕竟就是过条河的距离,习惯了。
// Cargo
type Cargo struct {Name stringHasBeenInCanada bool
}func (i *Cargo) HandleArrival(ev ArrivalEvent) {if ev.Port.Country == "Canada" {i.HasBeenInCanada = true}
}
把上面提到的cargo这个实体改一改,做点判断。
func (i *Ship) HandleLoad(ev LoadEvent) {for _, c := range i.Cargos {if c.Name == ev.Cargo.Name {panic("重复的货物我不接,这不是数据结构和算法,不要考虑特殊情况")}}i.Cargos = append(i.Cargos, ev.Cargo)
}func (i *Ship) HandleUnload(ev UnloadEvent) {// Suppose that there must have available cargo at the ship.for index, c := range i.Cargos {if c.Name == ev.Cargo.Name {i.Cargos = append(i.Cargos[1:index], i.Cargos[index+1:]...)break}}
}
Ship也要改一改,加上装卸货的方法。
// LoadEvent
type LoadEvent struct {DomainEventCargo *CargoShip *Ship
}func (i *LoadEvent) Process() {i.Ship.HandleLoad(*i)
}// UnloadEvent
type UnloadEvent struct {DomainEventCargo *CargoShip *Ship
}func (i *UnloadEvent) Process() {i.Ship.HandleUnload(*i)
}
加上装卸货的事件。
func TestCanada(t *testing.T) {eProc := NewEventProcessor()refact := &Cargo{Name: "Refactoring"}kr := &Ship{Name: "King Roy"}sfo := &Port{Name: "San Francisco", Country: "US"}la := &Port{Name: "Los Angeles", Country: "US"}yyv := &Port{Name: "Vancouver", Country: "Canada"}eProc.Process(&LoadEvent{DomainEvent: DomainEvent{Recorded: time.Now(),Occurred: time.Date(2005, time.November, 1, 0, 0, 0, 0, time.Local),},Cargo: refact,Ship: kr,})eProc.Process(&DepartureEvent{DomainEvent: DomainEvent{Recorded: time.Now(),Occurred: time.Date(2005, time.November, 1, 0, 0, 0, 0, time.Local),},Port: la,Ship: kr,})eProc.Process(&ArrivalEvent{DomainEvent: DomainEvent{Recorded: time.Now(),Occurred: time.Date(2005, time.November, 2, 0, 0, 0, 0, time.Local),},Port: yyv,Ship: kr,})eProc.Process(&DepartureEvent{DomainEvent: DomainEvent{Recorded: time.Now(),Occurred: time.Date(2005, time.November, 3, 0, 0, 0, 0, time.Local),},Port: yyv,Ship: kr,})eProc.Process(&ArrivalEvent{DomainEvent: DomainEvent{Recorded: time.Now(),Occurred: time.Date(2005, time.November, 4, 0, 0, 0, 0, time.Local),},Port: sfo,Ship: kr,})eProc.Process(&UnloadEvent{DomainEvent: DomainEvent{Recorded: time.Now(),Occurred: time.Date(2005, time.November, 4, 0, 0, 0, 0, time.Local),},Cargo: refact,Ship: kr,})fmt.Println(refact.HasBeenInCanada)
}
整体流程是这样的:先在LA装上货,去温哥华兜一圈,再回旧金山卸货。因为温哥华在加拿大,所以refact.HasBeenInCanada
字段为真。