Build support for has_one_through associations

Someday soon...

I'm not sure if "Someday soon..." means you're making fun of it or you're being serious. If you're serious it seems kind of vague to say "Someday soon..."

Will this be supported somewhen? I'm missing this. Is there a workaround?

@technoweenie: Has there been any talk about a has_one :through ? It seems the popular convention has been to manually define a one-line method instead. It's a hack, but it seems to work fine. Does anyone in core seem itching to add this association?

I've seen a few tickets requesting this type of feature. Although, it doesn't seem important enough for any of them to write a patch for it.

Please reopen once we have a patch to review.

The argument of, not implementing this because one-liner hacks are afloat, is of cause valid, but so is, I'd like to believe, the original ticket, and - may I add - modeling the real world will have you see this construct in a great many places.

Preferred contact amongst contacts

Preferred way of communication with a person amongst legend

and to not further ends, I could go on

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Anyways, I trembled over this: http://artofmission.com/articles/2007/6/21/has_one-through

Turns out, someone actually did take a stab at implementing the bugger, after all :)

I'm not fluent in "patchuese" so - I'll just reopen it, hoping for someone with a lot more patch_fu on his/her hands to take this one up the mountain and nail the son..

I've bunged together a patch with code shamelessly nicked from here: http://artofmission.com/articles/2007/6/21/has_one-through and here: http://idm.s9.xrea.com/ratio/2006/08/04/000496.html

In order to fulfill the requirements outlined in the description of this ticket you would implement the following:

class Person < ActiveRecord::Base
  has_one :primary_address, :through => :addressables, :conditions => ["addressable.primary = ?", true], :source => :addressable
end

Updated to simplify HasOneThroughAssociation (now inherits from HasManyThroughAssociation).

Also the through record is automatically created i.e.

class Member
  has_one :membership
  has_one club, :through => :membership
end

banana_man = Member.create
banana_man.club = Club.find_by_name("FLA")
#banana_man.membership automatically created

Latest patch ensures that replace works i.e.:

banana_man.club = Club.find_by_name("Banana fans")

banana_man.club = Club.find_by_name("Some other club")

I think this should include a test for the ":as" case.

Patch uploaded now includes test for polymorphic has_one :through

(In [9067]) Add has_one :through support, finally. Closes #4756 [thechrisoshow]

(In [9073]) Fix schema.rb some more. sponsors.sponsorable_type should be a string. References #4756.

tests no longer rely on implicit ordering (so pass with PostgreSQL)

(In [9075]) has_one :through supports :source_type. Fix up some tests. References #4756.