Laravel Migrations: Cannot add foreign key constraint

Question

I am trying to add foreign key constraints to my database tables via Laravel Migrations, but I always get an error like this:

Illuminate\Database\QueryException  :
SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint
(SQL: alter table `tasks` add constraint `tasks_task_list_id_foreign` foreign key (`task_list_id`) references `task_lists` (`id`))

The migration for the tasks table looks like this:

<?php

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

class CreateTasksTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('tasks', function (Blueprint $table) {
            $table->increments('id');
            $table->integer('user_id')->unsigned()->index();
            $table->integer('task_list_id')->unsigned()->index();
            $table->string('task');
            $table->timestamps();

            $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
            $table->foreign('task_list_id')->references('id')->on('task_lists');
        });
    }

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

And that's the task_lists table:

<?php

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

class CreateTaskListsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('task_lists', function (Blueprint $table) {
            $table->increments('id');
            $table->integer('user_id')->unsigned()->index();
            $table->string('name');
            $table->timestamps();

            $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
        });
    }

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

I can't figure out the problem and would highly appreciate any kind of help.

Thank you in advance!

Are you creating the `task_lists` table first? Are both tables using the `InnoDB` engine? — Jonas Staudenmeir, Oct 19 '18 at 17:42
Both are using `InnoDB`. The `task_lists` table is created after the `tasks` table. — jr-cologne, Oct 19 '18 at 17:47
Yeah, I guess that's the issue. Makes sense. But how can I change the order? — jr-cologne, Oct 19 '18 at 18:01

score 0 · Answer 1 · answered Oct 19 '18 at 17:45

You have to check the order of your migrations. Obviously, you have to run de Users table migration before the Tasks table migration. If the problem persist, try to make something like this inside the up() method and after the (Schemma::create):

    Schema::table('task_lists', function($table){
        $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
    });

Laravel Migrations: Cannot add foreign key constraint

1 Answers1