Rails - May 2010 - Can only traverse a polymorphic association in one direction

Hi all, I''m working on a polymorphic association and I''ve run
into a bit of a
stumbling block.  I only seem to be able to traverse the relationship in one
direction and not the other.  This is what my code looks like:


class NodeEntry < ActiveRecord::Base
  acts_as_nested_set
  belongs_to :node, :polymorphic => true
end

class Location < ActiveRecord::Base
    attr_accessor :name
    has_one :node_entry, :as => :node
    validates_presence_of :country, :region, :name
end

class Meter < ActiveRecord::Base
  attr_accessor :name, :parent_id
  has_one :node_entry, :as => :node
  validates_presence_of :meter_identifier, :type_of_meter
end

class MeterGroup < ActiveRecord::Base
  has_one :node_entry, :as => :node
end

When I create a new location or meter I use the following code:
@location = Location.new(params[:location])
@location_node = NodeEntry.new(:name => params[:location][:name])
@location_node.node = @location
@location_node.save

After loading a location or meter object from the database, when I attempt
to do a location.node I get an error saying the object doesn''t have
that
method.  When I load a node entry object I have no problem accessing its
node and I get the correct class back.

I can get around this by doing a simple query such as:
NodeEntry.first(:conditions => "node_id = #{loc.id} and node_type
''Location''").name

but I had assumed active record should be doing this for me under the
covers.  Have I made a mistake somewhere or is this the expected behavior of
polymorphic associations? 

-- 
View this message in context:
http://old.nabble.com/Can-only-traverse-a-polymorphic-association-in-one-direction-tp28692572p28692572.html
Sent from the RubyOnRails Users mailing list archive at Nabble.com.

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

On May 27, 7:18 am, BarryOg
<barryodrisc...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Hi all, I''m working on a polymorphic association and I''ve
run into a bit of a
> stumbling block.  I only seem to be able to traverse the relationship in
one
> direction and not the other.  This is what my code looks like:
>
> class NodeEntry < ActiveRecord::Base
>   acts_as_nested_set
>   belongs_to :node, :polymorphic => true
> end
>
> class Location < ActiveRecord::Base
>     attr_accessor :name
>     has_one :node_entry, :as => :node
>     validates_presence_of :country, :region, :name
> end
>
> class Meter < ActiveRecord::Base
>   attr_accessor :name, :parent_id
>   has_one :node_entry, :as => :node
>   validates_presence_of :meter_identifier, :type_of_meter
> end
>
> class MeterGroup < ActiveRecord::Base
>   has_one :node_entry, :as => :node
> end
>
> When I create a new location or meter I use the following code:
> @location = Location.new(params[:location])
> @location_node = NodeEntry.new(:name => params[:location][:name])
> @location_node.node = @location
> @location_node.save
>
> After loading a location or meter object from the database, when I attempt
> to do a location.node I get an error saying the object doesn''t
have that
> method.  
The has_one is still named what you''ve specified (:node_entry in this
case), the polymorphic stuff doesn''t change that...

So it''d be:

@location.node_entry

not

@location.node


--Matt Jones

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

Thanks for taking the time to read through my code and spot the obvious, I
guess too much coffee and too little sleep is not the best recipe.


Matt Jones wrote:
> 
> 
> The has_one is still named what you''ve specified (:node_entry in
this
> case), the polymorphic stuff doesn''t change that...
> 
> So it''d be:
> 
> @location.node_entry
> 
> not
> 
> @location.node
> 
> 
> --Matt Jones
> 
> -- 
> You received this message because you are subscribed to the Google Groups
> "Ruby on Rails: Talk" group.
> To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> To unsubscribe from this group, send email to
>
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> For more options, visit this group at
> http://groups.google.com/group/rubyonrails-talk?hl=en.
> 
> 
> 
-- 
View this message in context:
http://old.nabble.com/Can-only-traverse-a-polymorphic-association-in-one-direction-tp28692572p28765373.html
Sent from the RubyOnRails Users mailing list archive at Nabble.com.

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.