Dynamic finders in has_many associations

rubyonrails-talk
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

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(',')])

2. 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(',')])