问Grails域的通用beforeUpdate方法

EN

def init = { servletContext ->
         for (domainClass in grailsApplication.domainClasses) {
            if(domainClass.clazz.simpleName == domainName){
                domainClass.metaClass.beforeUpdate = {
                    println  "i am here "
                    def dirtyPropertyNames = this.getDirtyPropertyNames()
                    println(dirtyPropertyNames)
                    if(dirtyPropertyNames != null && dirtyPropertyNames.size() > 0) {

                        for (dirtyPropertyName in dirtyPropertyNames) {
                            def oldValue = (this.getPersistentValue((dirtyPropertyName)))
                            def newValue = (this."${dirtyPropertyName}")
                        }
                    }
                }
            }
        }
    }