Many to Many on Laravel migration

Question

I have 3 tables to connect each other. Tables name's roles, role_user, and users. I want to make migration on laravel and adding some constraint. and here's what in my role tables migration:

    Schema::create('roles', function (Blueprint $table) {
        $table->increments('id');
        $table->string('name');
        $table->string('description');
        $table->timestamps();
    });

and here's my Users table migration:

Schema::create('users', function (Blueprint $table) {
    $table->increments('id');
    $table->string('username')->unique();
    $table->string('name');
    $table->string('email')->unique();
    $table->string('password');
    $table->boolean('active')->default(0);
    $table->softDeletes();
    $table->rememberToken();
    $table->timestamps();
});

and here's my role_user table migration:

    Schema::create('role_user', function (Blueprint $table) {
        $table->integer('role_id')->unsigned();
        $table->integer('user_id')->unsigned();

        $table->unique(['role_id', 'user_id']);
        $table->foreign('role_id')->references('id')->on('roles')
            ->onDelete('cascade')->onUpdate('cascade');
        $table->foreign('user_id')->references('id')->on('users')
            ->onDelete('cascade')->onUpdate('cascade');
    });

in my Migration order i put roles table on top of users already but i got this kind of errors:

  [Illuminate\Database\QueryException]
  SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint (SQL: alter table `role_user` add constraint `role_user_role_id_foreign` foreign key (`role_id
  `) references `roles` (`id`) on delete cascade on update cascade)



  [PDOException]
  SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint

Solution

Probably your problem was with the order of creation of migrations.

Laravel runs the migrations in order of creation using the timestamp in the file name , because of that, if you created them in the following order:

1. roles in 2018_06_02_023539_create_roles_table
2. role_user in 2018_06_02_023800_create_role_user_table
3. users in 2018_06_02_023815_create_users_table

The table users would not exist when referenced in the table role_user, thus causing an SQL error. The most simple fix that you could do is renaming the role_user migration file in this way:

2018_06_02_023800_create_role_user_table => 2018_06_02_023820_create_role_user_table