How to bind data to a command object that has a nested property? (non domain object)

Question

I am trying to bind some data to an object that is part of a command object. The object stays null when trying to use it. Probably i am not giving the correct data in the gsp but i have no clue what am i doing wrong!

I would expect that when i submit a form with a field name 'book.title' this would get mapped into the command object.. but this fails.. The title stays [null]

Whenever i change the command object and form to use String title as property it works..

// the form that submits the data
<g:form>
   <g:textField name="book.title" value="Lord Of the Rings"/><br>
   <br><br>
   <g:actionSubmit action="create" value="Create!"/>
</g:form>


// the controller code
def create = { BooksBindingCommand cmd ->
   println cmd?.book?.title // the book property always stays null
   redirect(action: "index")
}

// the command object
class BooksBindingCommand {
   Book book
}

// the book class, simple plain groovy class
class Book {
   String title
}

Any suggestion on why the binding of 'book.title' fails?

Answer 1

Try to initialize it before binding, like:

// the command object
class BooksBindingCommand {
   Book book = new Book()
}

Answer 2

Just a quick stab at it.

The form field name should probably be book_title rather than using a period (not sure if it becomes a problem when handled in the controller).

<g:textField name="book_title" value="Lord Of the Rings"/><br>

In your controller, create your book model first, then assign it to the class you want it bound to.

def create = {
  def mybook = new Book()
  mybook.title = params.book_title
  def binder = new BooksBindingCommand()
  binder.book = mybook
}

Is the BooksBindingCommand a model? Because I'm not sure what you're trying to achieve.