Question

I have a ruby app that uses ActiveRecord. I have the following models

module ExchangeManager
  module Resources
    class Composition < ActiveRecord::Base
      belongs_to :chain
      belongs_to :link, :polymorphic => true, :primary_key => :id
    end

    class Chain < ActiveRecord::Base
      has_many :compositions
    end
  end
end

with the following migration

create_table :compositions do |t|
  t.references :link, :polymorphic => true
end

create_table :chains do |t|
  t.string :name, :null => false
end

When I create a new chain with 2 associated compositions, the SQL table ‘compositions’ contains :

id | link_id | link_type

1 | 1 | ExchangeManager::Resources::Chain

2 | 1 | ExchangeManager::Resources::Chain

Instead of having the full namespace in the link_type column, I would like ActiveRecord to save only the short Class Name, ie ‘Chain’ instead of ‘ExchangeManager::Resources::Chain’.

Why ? Because I am using the same DB in an another Rails app, and I would like to be able to manipulates the same models in that project without namespaces.

Answer 1

That would require, I presume, some patching of the polymorphic loading mechanism. And I would advise against it.

A better solution would be to have your own column which stores the type without the namespace.

class FirstModel
  before_save :store_link_type
  def store_link_type
    self.link_short_type = self.link && self.link.class.name.split(':').last # or whatever
    return true
  end
end

class SecondModel
  belongs_to :link, :polymorphic => true, :foreign_type => 'link_short_type'
end

If you want to update the link from the second app, too, you’ll have to do the reverse operation of prepending the namespace as well.