Working on tag name uniqueness

db/migrate/20110406203720_tag_name_uniqueness.rb

@@ -0,0 +1,37 @@
+class TagNameUniqueness < ActiveRecord::Migration
+  def self.downcase_tags
+    execute <<SQL
+      UPDATE tags
+      SET tags.name = LOWER(tags.name)
+      WHERE tags.name != LOWER(tags.name)
+SQL
+  end
+  def self.consolidate_duplicate_tags
+    duplicate_rows = execute <<SQL
+    SELECT count(tags.name), tags.name FROM tags
+      GROUP BY tags.name
+        HAVING COUNT(*) > 1
+SQL
+    duplicate_rows.each do |row|
+      name = row.last
+      tag_ids = execute("SELECT tags.id FROM tags WHERE tags.name = '#{name}'").to_a.flatten!
+      id_to_keep = tag_ids.pop
+      execute <<SQL
+              UPDATE taggings
+                SET taggings.tag_id = #{id_to_keep}
+                WHERE taggings.tag_id IN (#{tag_ids.join(',')})
+SQL
+      execute("DELETE tags WHERE tags.id IN (#{tag_ids.join(',')})")
+    end
+  end
+
+  def self.up
+    downcase_tags
+    consolidate_duplicate_tags
+    add_index :tags, :name, :unique => true
+  end
+
+  def self.down
+    raise ActiveRecord::IrreversibleMigration.new
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20110405170101) do
+ActiveRecord::Schema.define(:version => 20110406203720) do
 
   create_table "aspect_memberships", :force => true do |t|
     t.integer  "aspect_id",  :null => false