class PostTagLink < ActiveRecord::Base belongs_to :post belongs_to :tag end class CreatePostTagLinkTable < ActiveRecord::Migration[6.0] def change create_table :post_tag_links do |t| t.references :post, foreign_key: true, index: true t.references :tag, foreign_key: true, index: true end end end class Tag < ActiveRecord::Base belongs_to :post validates_presence_of :name end class CreateTagTable < ActiveRecord::Migration[6.0] def change create_table :tags do |t| t.string :name, null: false end end end