Dynamic finders in has_many associations

Rails
1

I have these 3 models.

class Ivr < ActiveRecord::Base
has_many :klusterings, :dependent => :destroy
has_many :klusters, :through => :klusterings, :uniq => true
end

class Kluster < ActiveRecord::Base
has_many :klusterings, :dependent => :destroy
has_many :ivrs, :through => :klusterings, :uniq => true
end

class Klustering < ActiveRecord::Base
belongs_to :kluster
belongs_to :ivr
end

I faced 2 problems and didn’t manage to find any good tutorial.

  1. Given some Kluster A, I want to find all the Ivrs that aren’t in A.
  2. I want to find all the Ivrs that aren’t in ANY Kluster.

– I managed to do 1. with:
@kluster = Kluster.find(params[:id])
@all_ivrs = Ivr.find(:all)

@ivrs = (@all_ivrs - @kluster.ivrs)

– And I did 2. with:
@all_ivrs = Ivr.find(:all).select{ |ivr| ivr.klusters.empty? }

But 1. does two SQL queries, one possibly very big (Ivr.find(:all)).
And 2. does that too.

Any way to do this, preferibly with dynamic finders?

2

On 24 Apr 2008, at 13:06, Paulo P. wrote:

I have these 3 models.

  1. Given some Kluster A, I want to find all the Ivrs that aren’t in A.
  2. I want to find all the Ivrs that aren’t in ANY Kluster.

You need some lower level stuff:

Ivr.find :all, :joins => ‘left outer join klusterings on
klusterings.ivr_id = ivrs.id’, :conditions => ‘kluster_id IS NULL’
finds ivrs associated with no klusters
Ivr.find :all, :joins => “left outer join klusterings on
klusterings.ivr_id = ivrs.id AND kluster_id =
#{@kluster.id}”, :conditions => ‘kluster_id IS NULL’
should find the ivrs not associated with @kluster
(typed quickly in mail, so might be slightly off, but should get you
there in the end)

Fred

3

I’ve done some similar lookups along these lines…

  1. Given some Kluster A, I want to find all the Ivrs that aren’t in A.
    @kluster = Kluster.find(…A…)
    @ivrs = Ivr.find(:all, :conditions=>[“id not in (?)”,
    @kluster.ivr_ids.join(‘,’)])
  1. I want to find all the Ivrs that aren’t in ANY Kluster.
    ivr_ids = Kluster.find(:all).collect{|kluster| kluster.ivr_ds}.uniq
    @unklustered = Ivr.find(:all, :conditions=>[“id not in (?)”,
    ivr_ids.join(‘,’)])

On Apr 24, 8:15 am, Frederick C. [email protected]