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copied!<p>The Rails way to do this is a named scope on pets.</p> <p>Something like this:</p> <pre><code>class Pets has_many :pet_names has_many :names, :through => :pet_names named_scope :with_current_name, lambda {|name| { :joins => "JOIN (pet_names pna, names) " + "ON (pna.pet_id = pets.id AND pna.name_id = names.id) " + "LEFT JOIN pet_names pnb " + "ON (pnb.pet_id = pets.id AND pna.created_at < pnb.created_at)", :conditions => ["pnb.id IS NULL AND names.id = ? ", name] } } end Pets.with_current_name(@name) @name.pets.with_current_name(@name) </code></pre> <p>To keep things name centric you could always define a method on C/Name that invokes the named scope.</p> <p>You could always do </p> <pre><code>class Name < ActiveRecord::Base has_many :pet_names has_many :pets, :through => :pet_names def currently_named_pets Pets.with_current_name(self) end end </code></pre> <p>And </p> <pre><code>@name.currently_named_pets </code></pre> <p>It's a pretty complicated join. Which is an indicator that you should probably should rethink the way you store this information. Why is it so important that Names be in a separate table? </p> <p>You might be better off doing something like this:</p> <p>After adding <code>name</code> and <code>old_name</code> columns to Pet:</p> <pre><code>class Pet < ActiveRecord::Base serialize :old_name, Array def after_initialization @old_name ||= [] end def name= new_name self.old_name << new_name self.name = new_name end named_scope :with_name, lambda {|name| { :conditions => {:name => name}} } end </code></pre>

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