Rendering command validation errors across a redirect

You can't send the command across in a redirect using params. You have a couple options:

• render() in the error condition instead of redirect()ing:

  if(cpmc.hasErrors()) {
      render(view: 'profile', model: [creditProvider: cpmc])
  }
  

  This is the most common idiom for what you're doing.

• Store the command in the session to persist it across the redirect:

  if(cpmc.hasErrors()) {
      session.cpmc = cpmc
      redirect(...)
  }
  
  // and in your action
  def cpmc = session.cpmc ?: null
  render(view: 'profile', model: [creditProvider: cpmc])
  

  This option is somewhat questionable. If not done correctly, you can pollute the session and leave objects hanging around, taking up memory. If done correctly, though, it can be a decent way to implement a post-redirect-get.