rails 4: problems with inheritance

Question

I probably didn't understand STI or whatever inheritance of rails :)

I need to implement a design where I have a form; on upload I submit, but if the user is not logged in, she needs to login via openid (only access supported). Thus this implies a redirect, and the best thing I could come up with so far is to temporarily save the data, and on successful login actually create the real object. I wanted to have two separate tables for the objects; the Site object is the one to be created, the Sitetmp is the temporary store, and it has an additional field called nonce; (on successful login, the nonce will be compared, and if ok, the Sitetmp instance deleted and a new Site one created)

The DB:

#schema.rb
 create_table "sites", force: true do |t|
    t.string   "name"
    t.date     "date"
    t.text     "description"
    t.float    "lat"
    t.float    "lon"
    t.date     "updated"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "sitetmps", force: true do |t|
    t.string "nonce"
    t.string "name"
    t.date   "date"
    t.text   "description"
  end

The Subclass:

#app/models/sitetmp.rb
class Sitetmp < Site
  attr_accessor :nonce
end

The Superclass:

#app/models/site.rb
class Site < ActiveRecord::Base
  validates :name, uniqueness: true, :presence => true,
                    :length => { :minimum => 5 }
  validates :date, :presence => true

  has_many :images, :inverse_of => :site
end

It seemed to be all set, but when I actually want to access the temporary object on successful login, it tells me

SQLite3::SQLException: no such column: sites.nonce: SELECT "sites".* FROM "sites" WHERE "sites"."nonce" = '059253928646750523787961570357' LIMIT 1

The code in the controller causing this is:

if nonce 
          @tmp = Sitetmp.find_by nonce: nonce

Clearly I am trying to access the Sitetmp instance by its nonce attribute, but rails is resolving to actually access the Site class - which doesn't have a nonce attribute.

What am I doing wrong? How do I correctly find the Sitetmp object by nonce in order to create a valid Site object from it?

bdx · Accepted Answer · 2014-09-18 05:45:53Z

As I understand it, ActiveRecord::Base has a table_name method. If you inherit from ActiveRecord::Base, the subclass (Site), through some rails magic, has the table_name set to the underscored lowercased version of itself.

Then inheriting from the Site class, Sitetmp does not get the advantage of having the table_name set.

You may be able to fix this by setting this:

#app/models/sitetmp.rb
class Sitetmp < Site
  # Set custom table name
  table_name "sitetmp"
  attr_accessor :nonce
end

I don't know if this would have an impact on the table_name of the Site class, so you may just have to create a standalone Sitetmp model to work from.

Alternatively, you could load the values into the session - see here for more

Actually, I accepted your response for the suggestion to create a standalone Sitetmp class, which I had done already :)

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