class CreateAnnotationDocuments < ActiveRecord::Migration[6.1]
  def change
    create_table :annotation_documents do |t|
      t.references  :annotation, null: false
      t.references  :document, null: false, polymorphic: true
      t.integer     :rank, null: false, default: 1

      t.timestamps
    end

    add_index :annotation_documents, 
              %i[annotation_id document_id document_type],
              name: "index_annotation_documents_uniqueness",
              unique: true
  end
end