4516_ticket.rb

# Following code has been tested with rails edge

class CreateUser < ActiveRecord::Migration
  def self.up
    create_table :users do |t|
      t.string :name
      t.string :type
    end
  end

  def self.down
    drop_table :users
  end
end

class User < ActiveRecord::Base
end

class Agent < User
end

class SuperAgent < Agent
end


rails c
> Agent.find_by_name 'agent'
SELECT "users".* FROM "users" WHERE ("users"."type" = 'Agent') AND ("users"."name" = 'agent') LIMIT 1
> SuperAgent # just load this class
> Agent.find_by_name 'agent'
SELECT "users".* FROM "users" WHERE (("users"."type" = 'Agent' OR "users"."type" = 'SuperAgent')) AND ("users"."name" = 'agent') LIMIT 1

# Note that in the above case by loading SuperAgent the sql generated 
# by Agent.find_by_name 'agent' has changed and now # the sql also includes SuperAgent

# However note that this behavior is not consistent if query is performed on the lowest level class.
rails c
> User.find_by_name 'agent'
SELECT "users".* FROM "users" WHERE ("users"."name" = 'agent') LIMIT 1
> Agent
> SuperAgent
> User.find_by_name 'agent'
SELECT "users".* FROM "users" WHERE ("users"."name" = 'agent') LIMIT 1


# Note that this is an issue only in development node. In production mode all the classes would be pre loaded.

In the first case SuperAgent is ORed because all superagents are agents. But of course AR needs to know about that class, otherwise it just does not have the information.

In the last case, User is the root of the hierarchy, and thus all records are users and no further constraints are needed. That is why you do not see the types ORed.