Finding all records that don't have child

rubyonrails-talk
1

I have two classes with a one-to-many relationship, and want to find all A records that don't have any B records. I can't seem to make a B.find(:all, :conditions => "blah") work because the foreign key is in A. Any help would be appreciated...

This is essentially what I have:

class A < ActiveRecord::Base   has_many :B end

class B < ActiveRecord::Base   belongs_to :A end

Am I going to have to do a :join to make this work with one sql statement? (Just to move on I wrote the following, but I know it is the wrong way to do it, just including so you can see the result I want to achieve.. )

  def self.no_B     ret = Array.new

    self.find(:all, :include => :B ).each do |a|       ret << a if a.B.empty?     end     ret   end

2

I would use a named_scope in this instance, assuming the relationship fields are completely normal.

So the field that u want to check is the association id is nil.

an example for that would be like this:

named_scope :unassociated, :conditions => "foreignkey_id IS NULL"

hope that works..