From: Robert Jones <jonesieboy@...>
Date: 2005-07-18T03:30:54+09:00
Subject: Re: Can Rails deal with related attributes in forms?

Kirk Haines wrote:

> On Saturday 16 July 2005 10:00 am, Robert Jones wrote:
> 
>> Suppose that object A has many of object B, and object B has some
>> attribute c, and that my Rails app has models that hold these
>> associations.
>>
>> Can Rails then help me to produce an edit form for object A that includes
>> a list of all the related object B's, and allows me to edit each of their
>> attribute c's directly (ie not by simply providing a link to a seperate
>> edit form for each of the object B's)
> 
> This doesn't seem to be a matter of "can" Rails do it.  The existing
> scaffolding may or may not be able to directly support this, but it should
> be darn simple to write something in any decent framework, with any decent
> ORM, that can.
> 
> I use a component in production that could trivially be extended to do
> exactly this, generically.
> 
> 
> Kirk Haines


I made it happen, pretty easily, but I still think this ought to be built
into Rails.  Can't see why it isn't.  Maybe it is and I'm missing
something.

I used an example of houses and rooms.  Each house has many rooms, and the
rooms have names.  In order to produce a form to edit the houses, which
allows direct editing of the names of the rooms in the house, I did the
following:

sql:

-------------------------------------------------------------
CREATE TABLE `houses` (
  `id` mediumint(9) NOT NULL auto_increment,
  `name` varchar(30) NOT NULL default '',
  `description` text NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ;

#
# Dumping data for table `houses`
#

INSERT INTO `houses` VALUES (1, 'Briary Bush', 'Lovely little house near a
babbling river');
INSERT INTO `houses` VALUES (2, 'Fawlty Towers', 'A grotty hell hole');

CREATE TABLE `rooms` (
  `id` mediumint(9) NOT NULL auto_increment,
  `name` varchar(50) NOT NULL default '',
  `house_id` mediumint(9) NOT NULL default '0',
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ;

#
# Dumping data for table `rooms`
#

INSERT INTO `rooms` VALUES (1, 'First Floor Front Room', 1);
INSERT INTO `rooms` VALUES (2, 'Penthouse', 1);
INSERT INTO `rooms` VALUES (3, 'Room 1', 2);

-------------------------------------------------------------


house.rb:

-------------------------------------------------------------
class House < ActiveRecord::Base
  has_many :rooms
  
 # This extends update_attributes to allow for the updating of the
associated records.
 # The "rooms" hash is in the form {"id"=>{"column"=>"value",.......},
"id"=>{"column"=>"value",.....},....}
  def update_attributes(attributes)
    attributes["rooms"].each do |key,value| 
      @room=Room.find(key)
      @room.update_attributes(value)
    end
    attributes.delete("rooms")
    super(attributes)
  end
end

-------------------------------------------------------------


room.rb:

-------------------------------------------------------------
class Room < ActiveRecord::Base
  belongs_to :house
end
-------------------------------------------------------------



_form.html partial in views/houses :

-----------------------------------------------------------
<%= error_messages_for 'house' %>

<!--[form:house]-->
<p><label for="house_name">Name</label><br/>
<%= text_field 'house', 'name'  %></p>

<p><label for="house_description">Description</label><br/>
<%= text_area 'house', 'description', "rows"=>"5"  %></p>
<% for room in @house.rooms %>
<label for="room_<%=room.id %>_name">Room <%=h room. id%></label>
<input id="house_rooms_<%=h room. id%>_name"  name="house[rooms][<%=h room.
id%>][name]" type="text" value="<%=h room. name%>" />
<% end %>
<!--[eoform:house]-->

-------------------------------------------------------------


I look forward to someone showing me a neater way to do it :)


The extension of the update_attributes method seems so simple that I can't
believe it would take much work to generalise this and have
update_attributes deal with associated data automatically.   Any takers for
this wee Rails development task ? ;)
-- 
Robert Jones