缘起

最近阅读 [Go微服务实战] (刘金亮, 2021.1)
本系列笔记拟采用golang练习之
git地址: https://gitee.com/ioly/learning.gooop

ES-CQRS模式

ES(Event Sourcing)事件溯源非常好理解，
指的是将每次的事件都记录下来，
而不是去记录对象的状态。
比如新建、修改等都会作为事件记录下来，
当需要最新的状态时，通过事件的堆叠来计算最新的状态。
按照事件溯源的模式进行架构设计，
就是事件驱动架构（Event DrivenArchitecture, EDA）。
命令查询职责分离（CQRS）最早来自Betrand Meyer写的
Object-OrientedSoftware Construction一书，
指的是命令查询分离（Command Query Separation,CQS）。
其基本思想是任何一个对象的方法都可以分为以下两大类:
▪ 命令（Command）：不返回任何结果（void），但会改变对象的状态。
▪ 查询（Query）：返回结果，但是不会改变对象的状态，对系统没有副作用。
CQRS的核心出发点就是把系统分为读和写两部分，从而方便分别进行优化。

目标(Day 1)

• 根据ES-CQRS模式, 设计”TODO - 待办事宜”程序

设计

• TodoDTO: 待办事宜数值对象
• TodoCreatedEvent: 创建todo事件
• TodoUpdatedEvent: 修改todo事件
• TodoRemovedEvent: 删除todo事件
• IEventBus: 事件总线接口
• iTodoEventSerializer: 事件序列化到JSON数据的接口
• iTodoReader: todo读取接口
• iTodoWriter: todo写入接口
• iJSONStore: json文件读写接口
• tEventBus: 事件总线的实现
• tTodoEventSerializer: 事件序列化到JSON的实现
• tTodoWriter: 事件写入器的实现
• tMockJSONStore: 虚拟的JSON文件读写实现
• tTodoReader: 未完成

TodoDTO.go

待办事宜数值对象

package todo_app
type TodoDTO struct {
    NO int
    Title string
    Content string
}

TodoCreatedEvent.go

todo事项创建事件

package todo_app
type TodoCreatedEvent struct {
    Data *TodoDTO
}

TodoUpdatedEvent.go

todo事项修改事件

package todo_app
type TodoUpdatedEvent struct {
    Data *TodoDTO
}

TodoRemovedEvent.go

todo事项删除事件

package todo_app
type TodoRemovedEvent struct {
    NO int
}

IEventBus.go

事件总线接口

package todo_app
type EventHandleFunc func(e string, args interface{})
type EventHandler struct {
    ID string
    Handler EventHandleFunc
}
type IEventBus interface {
    Pub(e string, args interface{})
    Sub(e string, id string, handleFunc EventHandleFunc)
    Unsub(e string, id string)
}
const EventTodoCreated = "todo.created"
const EventTodoUpdated = "todo.updated"
const EventTodoRemoved = "todo.removed"

iTodoEventSerializer.go

事件序列化到JSON数据的接口

package todo_app
type iTodoEventSerializer interface {
    SerializeCreatedEvent(it *TodoCreatedEvent) *tJSONData
    SerializeUpdatedEvent(it *TodoUpdatedEvent) *tJSONData
    SerializeRemovedEvent(it *TodoRemovedEvent) *tJSONData
}

iTodoReader.go

todo读取接口

package todo_app
type iTodoReader interface {
    All() []*TodoDTO
}

iTodoWriter.go

todo写入接口

package todo_app
type iTodoWriter interface {
    HandleCreated(e *TodoCreatedEvent)
    HandleUpdated(e *TodoUpdatedEvent)
    HandleRemoved(e *TodoRemovedEvent)
}

iJSONStore.go

json文件读写接口

package todo_app
type iJSONStore interface {
    Load()
    Append(it *tJSONData)
}

tEventBus.go

事件总线的实现

package todo_app
import (
    "learning/gooop/saga/mqs/logger"
    "sync"
)
type tEventBus struct {
    rwmutex *sync.RWMutex
    items map[string][]*EventHandler
}
func newEventHandler(id string, handleFunc EventHandleFunc) *EventHandler {
    return &EventHandler{
        id, handleFunc,
    }
}
func newEventBus() IEventBus {
    it := new(tEventBus)
    it.init()
    return it
}
func (me *tEventBus) init() {
    me.rwmutex = new(sync.RWMutex)
    me.items = make(map[string][]*EventHandler)
}
func (me *tEventBus) Pub(e string, args interface{}) {
    me.rwmutex.RLock()
    defer me.rwmutex.RUnlock()
    handlers,ok := me.items[e]
    if ok {
        for _,it := range handlers {
            logger.Logf("eventbus.Pub, event=%s, handler=%s", e, it.ID)
            go it.Handler(e, args)
        }
    }
}
func (me *tEventBus) Sub(e string, id string, handleFunc EventHandleFunc) {
    me.rwmutex.Lock()
    defer me.rwmutex.Unlock()
    handler := newEventHandler(id, handleFunc)
    handlers,ok := me.items[e]
    if ok {
        me.items[e] = append(handlers, handler)
    } else {
        me.items[e] = []*EventHandler{handler }
    }
}
func (me *tEventBus) Unsub(e string, id string) {
    me.rwmutex.Lock()
    defer me.rwmutex.Unlock()
    handlers,ok := me.items[e]
    if ok {
        for i,it := range handlers {
            if it.ID == id {
                lastI := len(handlers) - 1
                if i != lastI {
                    handlers[i], handlers[lastI] = handlers[lastI], handlers[i]
                }
                me.items[e] = handlers[:lastI]
            }
        }
    }
}
var GlobalEventBus = newEventBus()

tTodoEventSerializer.go

事件序列化到JSON的实现

package todo_app
type tTodoEventSerializer struct {
}
func newEventSeiralizer() iTodoEventSerializer {
    it := new(tTodoEventSerializer)
    return it
}
func (me *tTodoEventSerializer) serializeWithTag(tag int, v interface{}) *tJSONData {
    it := new(tJSONData)
    err := it.Set(TagCreated, v)
    if err != nil {
        return nil
    }
    return it
}
func (me *tTodoEventSerializer) SerializeCreatedEvent(e *TodoCreatedEvent) *tJSONData {
    return me.serializeWithTag(TagCreated, e)
}
func (me *tTodoEventSerializer) SerializeUpdatedEvent(e *TodoUpdatedEvent) *tJSONData {
    return me.serializeWithTag(TagUpdated, e)
}
func (me *tTodoEventSerializer) SerializeRemovedEvent(e *TodoRemovedEvent) *tJSONData {
    return me.serializeWithTag(TagRemoved, e)
}
const TagCreated = 1
const TagUpdated = 2
const TagRemoved = 3
var gDefaultEventSerializer = newEventSeiralizer()

tTodoWriter.go

事件写入器的实现

package todo_app
type tTodoWriter struct {
}
func newTodoWriter() iTodoWriter {
    it := new(tTodoWriter)
    it.init()
    return it
}
func (me *tTodoWriter) init() {
    GlobalEventBus.Sub("todo.created", "", me.handleEvent)
}
func (me *tTodoWriter) handleEvent(e string, args interface{}) {
    switch e {
    case EventTodoCreated:
        if it,ok := args.(*TodoCreatedEvent);ok {
            me.HandleCreated(it)
        }
        break
    case EventTodoUpdated:
        if it,ok := args.(*TodoUpdatedEvent);ok {
            me.HandleUpdated(it)
        }
        break
    case EventTodoRemoved:
        if it,ok := args.(*TodoRemovedEvent);ok {
            me.HandleRemoved(it)
        }
        break
    }
}
func (me *tTodoWriter) HandleCreated(e *TodoCreatedEvent) {
    j := gDefaultEventSerializer.SerializeCreatedEvent(e)
    if j != nil {
        MockJSONStore.Append(j)
    }
}
func (me *tTodoWriter) HandleUpdated(e *TodoUpdatedEvent) {
    j := gDefaultEventSerializer.SerializeUpdatedEvent(e)
    if j != nil {
        MockJSONStore.Append(j)
    }
}
func (me *tTodoWriter) HandleRemoved(e *TodoRemovedEvent) {
    j := gDefaultEventSerializer.SerializeRemovedEvent(e)
    if j != nil {
        MockJSONStore.Append(j)
    }
}

tMockJSONStore.go

虚拟的JSON文件读写实现

package todo_app
import "sync"
type tMockJSONStore struct {
    rwmutex *sync.RWMutex
    once sync.Once
    items []*tJSONData
}
func newMockJSONStore() iJSONStore {
    it := new(tMockJSONStore)
    it.init()
    return it
}
func (me *tMockJSONStore) init() {
    me.rwmutex = new(sync.RWMutex)
    me.items = []*tJSONData{}
}
func (me *tMockJSONStore) Load() {
    me.once.Do(func() {
        me.rwmutex.RLock()
        defer me.rwmutex.RUnlock()
        for _,it := range me.items {
            switch it.Tag {
            case TagCreated:
                v := new(TodoCreatedEvent)
                e := it.Get(v)
                if e == nil {
                    GlobalEventBus.Pub(EventTodoCreated, e)
                }
                break
            case TagUpdated:
                v := new(TodoUpdatedEvent)
                e := it.Get(v)
                if e == nil {
                    GlobalEventBus.Pub(EventTodoUpdated, e)
                }
                break
            case TagRemoved:
                v := new(TodoRemovedEvent)
                e := it.Get(v)
                if e == nil {
                    GlobalEventBus.Pub(EventTodoRemoved, e)
                }
                break
            }
        }
    })
}
func (me *tMockJSONStore) Append(it *tJSONData) {
    me.rwmutex.Lock()
    defer me.rwmutex.Unlock()
    me.items = append(me.items, it)
}
var MockJSONStore = newMockJSONStore()

(未完待续)