Coalesce favorites tables

db/migrate/20190220025517_coalesce_favorites_tables.rb

@@ -0,0 +1,43 @@
+class CoalesceFavoritesTables < ActiveRecord::Migration[5.2]
+  def up
+    create_table :temp_faves do |t|
+      t.integer :user_id, type: "integer"
+      t.integer :post_id, type: "integer"
+    end
+
+    # Remove the trigger and insert function
+    execute <<~SQL
+      DROP FUNCTION favorites_insert_trigger CASCADE;
+    SQL
+
+    # Copy data from all the descendant tables
+    execute <<~SQL
+      INSERT INTO temp_faves (user_id, post_id)
+      SELECT user_id, post_id FROM favorites;
+    SQL
+
+    # Add indexes and constraints after all the importing
+    # is done
+    add_index :temp_faves, :user_id
+    add_index :temp_faves, :post_id
+
+    change_column_null :temp_faves, :user_id, false
+    change_column_null :temp_faves, :post_id, false
+
+    add_foreign_key :temp_faves, :users
+    add_foreign_key :temp_faves, :posts
+
+    # Remove all the descendant tables
+    (0..99).each do |i|
+      drop_table "favorites_#{i}"
+    end
+
+    # Then remove the original and rename in place
+    drop_table :favorites
+    rename_table :temp_faves, :favorites
+  end
+
+  def down
+    fail ActiveRecord::IrreversibleMigration
+  end
+end