Drop the talks column from the TalkPreference model

app/models/talk_preference.rb

@@ -3,8 +3,6 @@ class TalkPreference < ActiveRecord::Base
 
   self.primary_key = :unique_id
 
-  serialize :talks, Array
-
   before_create :assign_new_unique_id
 
   def include?(id)
@@ -20,6 +18,10 @@ class TalkPreference < ActiveRecord::Base
     where created_at: timespan
   end
 
+  def talks
+    selected_talks.pluck :talk_id
+  end
+
   private
 
   def assign_new_unique_id

db/migrate/20161005115007_remove_talks_from_talk_preferences.rb

@@ -0,0 +1,26 @@
+class TalkPreference < ActiveRecord::Base
+  self.primary_key = :unique_id
+  has_many :selected_talks
+  serialize :talks, Array
+end
+
+class SelectedTalk < ApplicationRecord
+  belongs_to :talk_preference
+end
+
+class RemoveTalksFromTalkPreferences < ActiveRecord::Migration[5.0]
+  def up
+    remove_column :talk_preferences, :talks, :text
+  end
+
+  def down
+    add_column :talk_preferences, :talks, :text
+
+    talk_preferences = TalkPreference.all
+
+    talk_preferences.each do |preference|
+      preference.talks = preference.selected_talks.pluck(:talk_id)
+      preference.save!
+    end
+  end
+end