Rails - Feb 2010 - Finding all records that don't have child

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

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

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..
-- 
Posted via http://www.ruby-forum.com/.

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

That is finding all B records that have no parent. I want to find all A records
that have no child...

I''m thinking that the best/fastest way to do this would to just use
counters.


You wrote:

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..


      

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.