Rails - Feb 2006 - Error when using form helper and child objects

Hi,

This is one problem that has gotten me stumped for quite a while. I have 
an Item that has_many :DeliveryMethod, and what I seek to achieve is to 
create a form that''d let me create an Item, as well as its 
DeliveryMethods in 1 single form.

And so I tried something like:

<%= text_field_tag ''Item[DeliveryMethod][price]'', 
@Item.DeliveryMethod
? @Item.DeliveryMethod.price : nil %>

But I''ve received an application error
`@auction[DeliveryMethod][price]''
is not allowed as an instance variable name

Can someone please give me some pointers to what I might have 
overlooked? I got that format from an earlier posting in this mailing 
list, but it seems like I must have missed something.

Thank you.

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

On 2/4/06, Woei Shyang <woeishyang@gmail.com>
wrote:
> Hi,
>
> This is one problem that has gotten me stumped for quite a while. I have
> an Item that has_many :DeliveryMethod, and what I seek to achieve is to
> create a form that''d let me create an Item, as well as its
> DeliveryMethods in 1 single form.
>
> And so I tried something like:
>
> <%= text_field_tag ''Item[DeliveryMethod][price]'', 
@Item.DeliveryMethod
> ? @Item.DeliveryMethod.price : nil %>
>
> But I''ve received an application error
`@auction[DeliveryMethod][price]''
> is not allowed as an instance variable name
>
> Can someone please give me some pointers to what I might have
> overlooked? I got that format from an earlier posting in this mailing
> list, but it seems like I must have missed something.
>
A couple of things are going on here.
1. The form helpers are expecting to receive the names of instance
variables and methods (as strings) as their parameters.
text_field_tag ''Item[DeliveryMethod][price]'' is going to look
for an
instance variable called @Item[DeliveryMethod][price], which isn''t a
valid name.

2. Each call to text_field or text_field_tag will only emit one
<input> tag. You need to call it once for every field you need in the
output.

3. Item has_many DeliveryMethods, but you''re treating it as a has_one
in the above code.

This is roughly how I''d go about what you''ve described:
### models ###
class Item < ActiveRecord::Base
  has_many :delivery_methods
end

class DeliveryMethod < ActiveRecord::Base
  belongs_to :item
end

### controller ###
def show
  @item = Item.find params[:id]
end

### show.rhtml ###
# Other stuff here.. and then..
<%= text_field ''item'',
''some_method_that_item_has'' %>
<%= text_field ''item'',
''something_else_singular'' %>

<% if @item.delivery_methods -%>
  <%= render :partial => ''delivery_method'', :collection
=>
@item.delivery_methods %>
<% end -%>

### _delivery_method.rhtml ### (partial form)
<% @delivery_method = delivery_method -%> # The helpers require
instance methods, but the partial creates a local variable.
<% i = delivery_method_counter -%> # I hate typing
delivery_method_counter a dozen times.
<%= text_field ''delivery_method'',
''price'', :index => i %>

###
You can do this without partials, via @item.delivery_methods.each, or
a ''for'' loop, but I prefer the extra separation offered by the
partial
forms.
Notice the use of the :index => option, which lets Rails know you''re
making an array of fields.

In the controller, params[:delivery_method] will contain a hash of all
the delivery methods.
params[:delivery_method].each do |index, value|
  #index starts at ''0''
  #value contains whatever the user entered on the form.
end