My finder is insane. (.find returning wrong class?)

Question

Rails 3.2.11 MySql2 Gem

Hi, does anybody have an idea why my find method is returning an activerecord of the wrong type?

Here's the model:

class NameList < ActiveRecord::Base
  attr_accessible :name, :selected, :type
  self.table_name='name_lists'
end  

Here's the console output:

>> k=NameList.find(28)
NameList Load (0.0ms)  SELECT `name_lists`.* FROM `name_lists` WHERE `name_lists`.`id` = 28 LIMIT 1
#<Neighborhood id: 28, name: "Bayview">

>> k.class
Neighborhood(id: integer, city_id: integer, name: string, street_count: integer,  relative_value: float, home_count: integer, min_lot_size: integer, created_at: datetime, updated_at: datetime)

Notice that I am calling NameList.find, but what I get back is Neighborhood object. Oddly, the sql seems right -- its querying the NameList table.

There's nothing particularly special about the Neighborhood object: Here's the model for that:

class Neighborhood < ActiveRecord::Base
  belongs_to :city
  has_many :streets
  attr_accessible :name, :relative_value, :street_count
  def self.make(name, relative_value, min_lot_size, street_count, home_count)
     n=Neighborhood.new
     n.name = name
   end
 end

When I try to save it though -- it uses the definition of schema of Neighborhood and tries to update the wrong table.

> k.name = "Foo"
"Foo"

>> k.save
(1.0ms)  BEGIN
(0.0ms)  UPDATE `neighborhoods` SET `name` = 'Foo', `updated_at` = '2013-03-14 17:40:46' WHERE `neighborhoods`.`id` = 28
(0.0ms)  COMMIT
 true

Any ideas?

Answer 1

You have stumbled upon Rails Single Table Inheritance (STI), which you immediately get if you add a 'type' column to your table. Essentially the object is instantiated from the class whose name matches the value of the type column in that record.

If you want to learn about STI, read on here, look for the Single Table Inheritance section. In your case, I bet you don't really want that behavior, so your solution is to rename the column to something like kind, category, or whatever makes sense to you