Rails - Apr 2006 - Mapping contained objects to forms?

I''m having lots of trouble trying to map an object that contains
another
object to the right forms param.  So say I have Book which has one 
Publisher.  Here is what I''ve tried:

<p><label
for="book_publisher">Publisher</label><br/>
<%= text_field ''book'', ''publisher.name''
%> </p>

Then

<p><label
for="book_publisher">Publisher</label><br/>
<%= text_field ''book'', ''publisher[name]''
%> </p>

And

<p><label
for="book_publisher">Publisher</label><br/>
<%= text_field ''book.publisher'', ''name''
%> </p>

All of them blow up with various exceptions.  What is the right way to 
map a many to one relationship onto a form?  And how will it know the ID 
of the contained object if it just has the name on the form?  Is there 
something else I have to do to put the Publisher''s ID on the form so I 
can remember it?  The Agile Web Development with Rails book is not 
helpful on this issue.

Charlie

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Posted via http://www.ruby-forum.com/.

Bump.  Any ideas?  I''m sure someone knows how this works.


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Posted via http://www.ruby-forum.com/.

On 4/11/06, Charlie <charlie.hubbard@gmail.com>
wrote:
> I''m having lots of trouble trying to map an object that contains
another
> object to the right forms param.  So say I have Book which has one
> Publisher.  Here is what I''ve tried:
>
> <p><label
for="book_publisher">Publisher</label><br/>
> <%= text_field ''book'',
''publisher.name'' %> </p>
You cannot do the dotted method call with the standard Rails helpers
AFAIK.  I got frustrated with not being about to do this so wrote a
helper for it (there are probably loads of better ways to achieve this
but it got me going).  My ''custom_text_field'' generates a text
field
with a name of book[publisher][name] for your call.

I''m not entirely sure why this isn''t supported by Rails
out-of-the-box.

Matt

class TagHelper
  def custom_text_field(object_id, method, options = { })
    text_field_tag(
      object_field_name(object_id, method),
      object_value(object_id, method),
      options
    )
  end

  def object_value(object_id, method)
    method.split(".").inject(self.instance_variable_get("@#{
object_id
}")) { |o,m| o.nil? ? nil : o.send(m) }
  end

  def object_field_name(object_id, method)
    method.split(".").inject(object_id) { |f,n| "#{ f }[#{ n
}]" }
  end
end