[Rails] Can only traverse a polymorphic association in one direction

[BarryOg]

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?

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[Matt Jones]

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

[BarryOg]

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
>

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