Rails - Jun 2008 - unidirectional belongs_to polymorphic

The setup:
class Location::Base < ActiveRecord::Base
  set_table_name :locations
  ...
end
class Location::Address < Location::Base
  ...
end
class Location::Airport < Location::Base
  ...
end
class Person < ActiveRecord::Base
  belongs_to :location, :polymorphic => true, :class_name =>
"Location::Base"
  ...
end

I want a unidirectional belongs_to relationship.  That is, Locations
are never going to need to figure out who''s at them.  Or, more
specifically, the headache involved with the many-to-many and the
caching and everything isn''t worth the cost.  I just want to be able
to store a location for a Person (and for various other models that
are unrelated to Person).

Some questions:

Why does Person need both a location_id and a location_type?  In order
to instantiate the location, it needs to look up the whole row in the
locations table, which includes a "type" column (as required by single
table inheritance).

Why won''t the new sexy fixtures work on this (regardless of whether
Person has a location_type column)?  They seem to work only if
Location::Base has_one :person.

-Gaius
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Right, so the answer is that uni-directional belongs_to associations
*can''t* be polymorphic.  The polymorphicness of a belongs_to
association is on the belonging-to side, not the belonged-side.  That
is, my Person doesn''t inherit from some "Locatable."

This solves it:
class Person < ActiveRecord::Base
  belongs_to :location, :class_name => ''Location::Base''
end

(I actually do abstract Locatable into a mixin module, but it''s not an
STI inheritance thing, so there''s no AR polymorphism.)

-Gaius

On Jun 11, 8:18 pm, gcnovus
<james.a.ro...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> The setup:
> class Location::Base < ActiveRecord::Base
>   set_table_name :locations
>   ...
> end
> class Location::Address < Location::Base
>   ...
> end
> class Location::Airport < Location::Base
>   ...
> end
> class Person < ActiveRecord::Base
>   belongs_to :location, :polymorphic => true, :class_name =>
> "Location::Base"
>   ...
> end
>
> I want a unidirectional belongs_to relationship.  That is, Locations
> are never going to need to figure out who''s at them.  Or, more
> specifically, the headache involved with the many-to-many and the
> caching and everything isn''t worth the cost.  I just want to be
able
> to store a location for a Person (and for various other models that
> are unrelated to Person).
>
> Some questions:
>
> Why does Person need both a location_id and a location_type?  In order
> to instantiate the location, it needs to look up the whole row in the
> locations table, which includes a "type" column (as required by
single
> table inheritance).
>
> Why won''t the new sexy fixtures work on this (regardless of
whether
> Person has a location_type column)?  They seem to work only if
> Location::Base has_one :person.
>
> -Gaius
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