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?


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On May 27, 7:18 am, BarryOg [email protected] wrote:

attr_accessor :name

class MeterGroup < ActiveRecord::Base
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 J.

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 J. wrote:

[email protected]
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.


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