class Part < ActiveRecord::Base
has_many :components # or, maybe not
class Lot < ActiveRecord::Base
class Component < ActiveRecord::Base
belongs_to :part # or, maybe not
In my domain, a "lot" of "components" has a part number (which I
represent in RoR as a #belongs_to relationship, even though the term
"belongs_to" is somewhat misleading). Each component in the lot has a
part number which is the same as the part number for the entire lot.
What is the best way to ensure that this consistency is maintained?
That is, that all parts in a lot reference the same part number as the
One way to ensure the consistency is to remove the "part_id" column
from the component table and to reference a components part number
through the lot association, i.e. mycomponent.lot.part.number. The
problem is, sometimes I want to look at all of the parts that have a
given part number, and the only way I can see to do that is to collect
all of the lots with a given part number and then collect all of the
components in each of the lots, using something like:
mypart.lots.map(&:components).flatten. Unfortunately, that returns an
array of components instead of the dynamic finder that would be
returned by mypart.components.
A second way to ensure the consistency is to add validations to the
Lot and/or Component models. I could do that, but I have been advised
elsewhere that validations are best when augmented by database
if you are interested). Is there some database agnostic way to add
this sort of constraint?
Or is there some other mechanism to implement this?