Multiple column foreign keys / associations in ActiveRecord/Rails - mysql

Question

I have badges (sorta like StackOverflow).
Some of them can be attached to badgeable things (e.g. a badge for >X comments on a post is attached to the post). Almost all come in multiple levels (e.g. >20, >100, >200), and you can only have one level per badgeable x badge type (= badgeset_id).
To make it easier to enforce the one-level-per-badge constraint, I want badgings to specify their badge by a two-column foreign key - badgeset_id and level - rather than by primary key (badge_id), though badges does have a standard primary key too.
In code:
class Badge < ActiveRecord::Base
has_many :badgings, :dependent => :destroy
# integer: badgeset_id, level
validates_uniqueness_of :badgeset_id, :scope => :level
end
class Badging < ActiveRecord::Base
belongs_to :user
# integer: badgset_id, level instead of badge_id
#belongs_to :badge # <-- how to specify?
belongs_to :badgeable, :polymorphic => true
validates_uniqueness_of :badgeset_id, :scope => [:user_id, :badgeable_id]
validates_presence_of :badgeset_id, :level, :user_id
# instead of this:
def badge
Badge.first(:conditions => {:badgeset_id => self.badgeset_id, :level => self.level})
end
end
class User < ActiveRecord::Base
has_many :badgings, :dependent => :destroy do
def grant badgeset, level, badgeable = nil
b = Badging.first(:conditions => {:user_id => proxy_owner.id, :badgeset_id => badgeset,
:badgeable_id => badgeable.try(:id), :badgeable_type => badgeable.try(:class)}) ||
Badging.new(:user => proxy_owner, :badgeset_id => badgeset, :badgeable => badgeable)
b.level = level
b.save
end
end
has_many :badges, :through => :badgings
# ....
end
How I can specify a belongs_to association that does that (and doesn't try to use a badge_id), so that I can use the has_many :through?
ETA: This partially works (i.e. #badging.badge works), but feels dirty:
belongs_to :badge, :foreign_key => :badgeset_id, :primary_key => :badgeset_id, :conditions => 'badges.level = #{level}'
Note that the conditions is in single quotes, not double, which makes it interpreted at runtime rather than loadtime.
However, when trying to use this with the :through association, I get the error undefined local variable or method 'level' for #<User:0x3ab35a8>. And nothing obvious (e.g. 'badges.level = #{badgings.level}') seems to work...
ETA 2: Taking EmFi's code and cleaning it up a bit works. It requires adding badge_set_id to Badge, which is redundant, but oh well.
The code:
class Badge < ActiveRecord::Base
has_many :badgings
belongs_to :badge_set
has_friendly_id :name
validates_uniqueness_of :badge_set_id, :scope => :level
default_scope :order => 'badge_set_id, level DESC'
named_scope :with_level, lambda {|level| { :conditions => {:level => level}, :limit => 1 } }
def self.by_ids badge_set_id, level
first :conditions => {:badge_set_id => badge_set_id, :level => level}
end
def next_level
Badge.first :conditions => {:badge_set_id => badge_set_id, :level => level + 1}
end
end
class Badging < ActiveRecord::Base
belongs_to :user
belongs_to :badge
belongs_to :badge_set
belongs_to :badgeable, :polymorphic => true
validates_uniqueness_of :badge_set_id, :scope => [:user_id, :badgeable_id]
validates_presence_of :badge_set_id, :badge_id, :user_id
named_scope :with_badge_set, lambda {|badge_set|
{:conditions => {:badge_set_id => badge_set} }
}
def level_up level = nil
self.badge = level ? badge_set.badges.with_level(level).first : badge.next_level
end
def level_up! level = nil
level_up level
save
end
end
class User < ActiveRecord::Base
has_many :badgings, :dependent => :destroy do
def grant! badgeset_id, level, badgeable = nil
b = self.with_badge_set(badgeset_id).first ||
Badging.new(
:badge_set_id => badgeset_id,
:badge => Badge.by_ids(badgeset_id, level),
:badgeable => badgeable,
:user => proxy_owner
)
b.level_up(level) unless b.new_record?
b.save
end
def ungrant! badgeset_id, badgeable = nil
Badging.destroy_all({:user_id => proxy_owner.id, :badge_set_id => badgeset_id,
:badgeable_id => badgeable.try(:id), :badgeable_type => badgeable.try(:class)})
end
end
has_many :badges, :through => :badgings
end
While this works - and it's probably a better solution - I don't consider this an actual answer to the question of how to do a) multi-key foreign keys, or b) dynamic-condition associations that work with :through associations. So if anyone has a solution for that, please speak up.

Answer 1

Seems like it might workout best if you separate Badge into two models. Here's how I'd break it down to achieve the functionality you want. I threw in some named scopes to keep the code that actually does things clean.
class BadgeSet
has_many :badges
end
class Badge
belongs_to :badge_set
validates_uniqueness_of :badge_set_id, :scope => :level
named_scope :with_level, labmda {|level
{ :conditions => {:level => level} }
}
named_scope :next_levels, labmda {|level
{ :conditions => ["level > ?", level], :order => :level }
}
def next_level
Badge.next_levels(level).first
end
end
class Badging < ActiveRecord::Base
belongs_to :user
belongs_to :badge
belongs_to :badge_set
belongs_to :badgeable, :polymorphic => true
validates_uniqueness_of :badge_set_id, :scope => [:user_id, :badgeable_id]
validates_presence_of :badge_set_id, :badge_id, :user_id
named_scope :with_badge_set, lambda {|badge_set|
{:conditions => {:badge_set_id => badge_set} }
}
def level_up(level = nil)
self.badge = level ? badge_set.badges.with_level(level).first
: badge.next_level
save
end
end
class User < ActiveRecord::Base
has_many :badgings, :dependent => :destroy do
def grant badgeset, level, badgeable = nil
b = badgings.with_badgeset(badgeset).first() ||
badgings.build(
:badge_set => :badgeset,
:badge => badgeset.badges.level(level),
:badgeable => badgeable
)
b.level_up(level) unless b.new_record?
b.save
end
end
has_many :badges, :through => :badgings
# ....
end