How to setup a casbin watcher along with the the Gorm adapter about gorm-adapter HOT 4 CLOSED

package main

import (
	"fmt"
	"github.com/casbin/casbin/v2"
	gormadapter "github.com/casbin/gorm-adapter/v3"
	_ "github.com/go-sql-driver/mysql"
)

type SampleWatcher struct {
	callback func(string)
}

func myCallBack(s string) {
	fmt.Println(s)
}
func (w *SampleWatcher) Close() {
}

func (w *SampleWatcher) SetUpdateCallback(callback func(string)) error {
	w.callback = callback
	return nil
}

func (w *SampleWatcher) Update() error {
	if w.callback != nil {
		fmt.Println("watcher Update")
		w.callback("myCallBack")
	}
	return nil
}

func main() {
	a, _ := gormadapter.NewAdapter("mysql", "root:root@tcp(127.0.0.1:3307)/") // Your driver and data source.
	e, _ := casbin.NewEnforcer("examples/rbac_model.conf", a)

	//e, _ := casbin.NewEnforcer("examples/rbac_model.conf", "examples/rbac_policy.csv")

	sampleWatcher := &SampleWatcher{}
	_ = e.SetWatcher(sampleWatcher)
	_ = sampleWatcher.SetUpdateCallback(myCallBack)
	e.EnableAutoNotifyWatcher(true)

	_ = e.SavePolicy() //calls watcher.Update()
}