#1955: Migrate tags to belong to named users for enhanced privacy.

db/migrate/20190618202817_add_user_id_to_tag.rb

@@ -0,0 +1,72 @@
+class AddUserIdToTag < ActiveRecord::Migration[5.2]
+  def self.up
+	  add_column :tags, :user_id, :integer
+
+	  # Find uses of each tag for both Todos and RecurringTodos to
+	  # figure out which users use which tags.
+	  @tags = execute <<-EOQ
+		  SELECT t.id AS tid, tds.user_id AS todo_uid, rt.user_id AS rtodo_uid
+		  FROM tags t
+		  JOIN taggings tgs ON tgs.tag_id = t.id
+		  LEFT OUTER JOIN todos tds
+		   ON tgs.taggable_type = "Todo" AND tds.id = tgs.taggable_id
+		  LEFT OUTER JOIN recurring_todos rt
+		   ON tgs.taggable_type = "RecurringTodo" AND rt.id = tgs.taggable_id
+		  WHERE rt.id IS NOT NULL OR tds.id IS NOT NULL
+		  GROUP BY t.id, tds.user_id, rt.user_id
+	  EOQ
+
+	  # Map each tag to the users using it.
+	  @tag_users = {}
+	  @tags.each do |row|
+		  uid = (row[1] ? row[1] : row[2])
+		  if not @tag_users[row[0]]
+		    @tag_users[row[0]] = [uid]
+		  elsif not @tag_users[row[0]].include? uid
+		    @tag_users[row[0]] << uid
+		  end
+	  end
+
+	  # Go through the tags assigning users and duplicating as necessary.
+	  @tag_users.each do |tid, uids|
+		tag = Tag.find(tid)
+
+		# One of the users will get the original tag instance, but first
+		# duplicate their own copy to all the others.
+		extras = uids.length - 1
+		extras.times do |n|
+		  uid = uids[n+1]
+
+		  # Create a duplicate of the tag assigned to the user.
+		  new_tag = tag.dup
+		  new_tag.user_id = uid
+		  new_tag.save!
+
+		  # Move all the user's regular todos to the new tag.
+			connection.execute(<<-EOQ)
+			  UPDATE taggings ta
+			  JOIN todos t
+			   ON ta.taggable_type = "Todo" AND t.id = ta.taggable_id
+			  SET ta.tag_id = #{new_tag.id}
+			  WHERE t.user_id = #{uid}
+		  EOQ
+
+		  # Move all the user's recurring todos to the new tag.
+		  connection.execute(<<-EOQ)
+			  UPDATE taggings ta
+			  JOIN recurring_todos t
+			   ON ta.taggable_type = "RecurringTodo" AND t.id = ta.taggable_id
+			  SET ta.tag_id = #{new_tag.id}
+			  WHERE t.user_id = #{uid}
+		  EOQ
+		end
+
+		tag.user_id = uids[0]
+		tag.save!
+	  end
+  end
+  def self.down
+      remove_column :tags, :user_id
+  end
+end
+

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2016_01_31_233303) do
+ActiveRecord::Schema.define(version: 2019_06_18_202817) do
 
   create_table "attachments", options: "ENGINE=InnoDB DEFAULT CHARSET=utf8", force: :cascade do |t|
     t.integer "todo_id"
@@ -159,6 +159,7 @@ ActiveRecord::Schema.define(version: 2016_01_31_233303) do
     t.string "name"
     t.datetime "created_at"
     t.datetime "updated_at"
+    t.integer "user_id"
     t.index ["name"], name: "index_tags_on_name"
   end