How to solve Globalize3 issue with old migrations when adding translated fields

_README

There's an issue on globalize when adding or removing fields from the translations that causes the original migrations don't work properly (https://github.com/svenfuchs/globalize3/issues/131).

In my example I have a post model whih I create with some translated fields: name, slug and body. Some days later, I realise I need an excerpt field with a summarized version of the post and it has to be translated, so I create a migration to add this field.

Unfortunately, when you create the translation table it takes not only the fields you set in the params (:name => :string, :slug => :string, :body => :text) but also the params specified to the translates method in the model (:excerpt included) and creates a column for each one of those.

Solution here is to overwrite the translated attribute names of the class in the migration, so when you execute a migration you know which translated attributes will be declared and not need to worry about attributes that are not declared when you create the migration.

Overwriting these attributes is as simple as Post.translated_attribute_names = [:name, :slug, :body]

It's only necessary for the original creation migration, as there's no easy way to add translated fields to the translation table (https://github.com/svenfuchs/globalize3/issues/98), but I think it could be useful to explictly point out what translated fields exist at the moment you add a new column to the translations table.

It could be quite simple to fork the project and create a patch based on this simple idea, but while I find the time to do it I think this may help some people out there.

* Migrations are modifications of a real project and may not be fully functional as they have not really been tested. What I have tested is the idea of overwriting the translated_attributes and it works fine.

app_models_post.rb

class Post
  translates  :name, :slug, :body, :excerpt
end

db_migrate_20120827135326_add_excerpt_to_post.rb

class AddExcerptToPost < ActiveRecord::Migration
  def up

    Post.translated_attribute_names = [:name, :slug, :body, :excerpt]
    add_column :post_translations, :excerpt, :string

  end

  def down
    remove_column :post_translations, :excerpt

  end
end

db_migrate_20120827135326_add_excerpt_to_post.rb.WRONG

class AddExcerptToPost < ActiveRecord::Migration
  def up
    add_column :post_translations, :excerpt, :string
  end

  def down
    remove_column :post_translations, :excerpt
  end

end

db_migration_20120827134400_create_posts.rb

class CreatePosts < ActiveRecord::Migration

  def up
    create_table :posts do |t|
      t.string :author

      t.timestamps
    end

    Post.translated_attribute_names = [:name, :slug, :body]
    Post.create_translation_table! :name => :string, :slug => :string, :body => :text

  end

  def down

    drop_table :posts

    Post.drop_translation_table!

  end

end

db_migration_20120827134400_create_posts.rb.wrong

class CreatePosts < ActiveRecord::Migration

  def up
    create_table :posts do |t|
      t.string :author

      t.timestamps
    end

    Post.create_translation_table! :name => :string, :slug => :string, :body => :text

  end

  def down

    drop_table :posts

    Post.drop_translation_table!

  end

end