Paste for http://laravel.io/forum/04-26-2015-weird-sql-error-while-trying-to-remove-related-object

migration.php

<?php

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

class CreateCategoriesTableWithI18n extends Migration {

	/**
	 * Run the migrations.
	 *
	 * @return void
	 */
	public function up()
	{
		Schema::create('categories', function(Blueprint $table)
		{
			$table->increments('id');
			//
			$table->unsignedInteger('parent_id')->nullable();
			$table->foreign('parent_id')
				->references('id')
				->on('categories')
				->onUpdate('cascade')
				->onDelete('set null');
			$table->string('title');
			//
			$table->timestamps();
		});

	}

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

}

model.php

<?php namespace App;

use Illuminate\Database\Eloquent\Model;

class Category extends Model {

	protected $table = 'categories';

	protected $fillable = [
		'parent_id',
		'title',
	];

}