Rails - Sep 2009 - Populating parent relationships automagically

I would like to populate parent relationships when I load children
objects.  I have a relatively complex object graph.  Something like:
Thing <1-*> Components <1-*> Assembly <*-*> Parts

The notion is that we allow a Thing to be designed with ''construction
issues'', but can''t be ''manufactured'' until
it doesn''t have any issues.
There can be issues at any level.  A Thing can have too many
components.  A component can have the wrong kinds of Assemblies.  So
far, so good.

The problem comes in where there are complex grouping rules.  There
are grouping rules for Parts that depend on how many of the same Part
exist within the entire Thing, for example.

When I fetch, I do something like
Thing.find(some_id, :includes => {:components => {:assmeblies
=> :parts}})
and that works fine.

But when I want to display some of the errors associated with a Part,
I have to reach back up to Thing to find some of the issues.

part.assembly.component.thing will return a different object for every
part.

So I''m interested in a plugin or some code that will populate the
parent relationships when the children objects are loaded.  Then I''ll
be able to traverse relationships up and down without proliferating
objects.

Or other architectural suggestions.

On Sep 30, 11:26 am, "kwe...-e+AXbWqSrlAAvxtiuMwx3w@public.gmane.org"
<kurt.we...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> I would like to populate parent relationships when I load children
> objects.  I have a relatively complex object graph.  Something like:
> Thing <1-*> Components <1-*> Assembly <*-*> Parts
>
>
> part.assembly.component.thing will return a different object for every
> part.
>
Most likely you are maintaining a many to many relationship table
between <% :parts %> and <% :assemblies %>. That means a single Part
can be associated with multiple Assembly.

As you wrote: <% part.assembly.component.thing %>

In the above call <% part.assemble %> will return array of assembles
and you can not call <% .component %> on that array.

You need to distinguish between the Assemblies of a single Part to
reach up to its'' Thing.
Would you please give some of your sample associations and the
scenario where you need to call <% part.assembly.component.thing %>?
Hope i can provide something more specific.

Thank you

On Sep 29, 10:48 pm, Samiron
<samironp...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> On Sep 30, 11:26 am,
"kwe...-e+AXbWqSrlAAvxtiuMwx3w@public.gmane.org"
<kurt.we...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > I would like to populate parent relationships when I load children
> > objects.  I have a relatively complex object graph.  Something like:
> > Thing <1-*> Components <1-*> Assembly <*-*> Parts
>
> > part.assembly.component.thing will return a different object for every
> > part.
>
> Most likely you are maintaining a many to many relationship table
> between <% :parts %> and <% :assemblies %>. That means a single
Part
> can be associated with multiple Assembly.
>
> As you wrote: <% part.assembly.component.thing %>
>
> In the above call <% part.assemble %> will return array of assembles
> and you can not call <% .component %> on that array.
You''re right, I botched my analogy.  It is assembly that is reaching
up.
> Would you please give some of your sample associations and the
> scenario where you need to call <% part.assembly.component.thing %>?
> Hope i can provide something more specific.
Supposing that
def Thing#assemblies
  components.map(&:assemblies).flatten.uniq
end

def Assembly#manufacturing_issues
  issues = []
  ...
  if component.thing.assemblies.map(&:type).include?(conflicting_type)
    issues << "Can not have a #{conflicting_type} in the same
thing."
  end
  ...
  issues
end

Here we have an assembly reaching up to its Thing to find out if any
of its peers is of conflicting type.  Keep in mind that I want this
issue to be displayed with the Assembly - so this is where I put the
logic.  Also it seems reasonable to keep it here since it is knowledge
of the Assembly types that defines whether or not it conflicts.

Since parent relationships are not populated, we''re going to get a
different Thing - which means that Thing is going to need to load
*all* its assemblies just to see if there is one that conflicts.  I''d
like to be able to traverse the object graph and get to the Thing that
caused this Assembly to load - that way I would be using the same
objects; no additional loads needed..