bookstack/database/migrations/2022_08_17_092941_create_references_table.php

<?php

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

return new class extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('references', function (Blueprint $table) {
            $table->id();
            $table->unsignedInteger('from_id')->index();
            $table->string('from_type', 25)->index();
            $table->unsignedInteger('to_id')->index();
            $table->string('to_type', 25)->index();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('references');
    }
};