GORM insert and update auto-set of createUser and updateUser

Our company has a standard of using the following attributes on all database tables:

 String createUser 
 Date createDate  
 String updateUser 
 Date updateDate 

But we did not want to put code in all controller's to set these fields on insert or update. Grails has a nice facilities where you specify code in the beforeInsert and beforeUpdate closures to set the dates:

 def beforeInsert = {
  createDate = new Date()
 }
 def beforeUpdate = {
  updateDate = new Date()
 }

Grails will call these closures automatically. But the issue is setting the createUser and updateUser. What we did is create an abstract base class (concrete makes Grails look for a table called base):

abstract class Base {
  
 String createUser = ''
 Date createDate = new Date()
 String updateUser = '' 
 Date updateDate = new Date()

 def beforeInsert = {
  setCreateUsername() // must be injected in login controller
  createDate = new Date()
  delegate.createUser = this.createUser
  delegate.updateUser = this.updateUser
 }
 
 def beforeUpdate = {
  setUpdateUsername() // must be injected in login controller
  updateDate = new Date()
  delegate.updateUser = this.updateUser
 }
}

Each of our domain classes extended Base (so they did not have to specify the 4 fields.)
Then, when the user login is handled by the Login controller, we inject the setCreateUsername and updateUsername "methods" as closures that set the username with the HttpSession value:

def user = User.findWhere(userId:params.userId, userPwd:params.userPwd)
session.user = user 
Base.metaClass.setCreateUsername = {
  createUser = session.user.userId
  updateUser = session.user.userId
}
Base.metaClass.setUpdateUsername = {
  updateUser = session.user.userId
}

And the four columns are automatically set on all insert and updates.