Laravel 5.1 Migration and Seeding Cannot truncate a table referenced in a foreign key constraint - mysql

Question

I'm trying to run the migration (see below) and seed the database, but when I run
php artisan migrate --seed
I get this error:
Migration table created successfully.
Migrated: 2015_06_17_100000_create_users_table
Migrated: 2015_06_17_200000_create_password_resets_table
Migrated: 2015_06_17_300000_create_vehicles_table
[Illuminate\Database\QueryException]
SQLSTATE[42000]: Syntax error or access violation: 1701 Cannot truncate a table
referenced in a foreign key constraint (`app`.`vehicles`, CONSTRAINT `vehic
les_user_id_foreign` FOREIGN KEY (`user_id`) REFERENCES `app`.`users` (`id`
)) (SQL: truncate `users`)
[PDOException]
SQLSTATE[42000]: Syntax error or access violation: 1701 Cannot truncate a table
referenced in a foreign key constraint (`app`.`vehicles`, CONSTRAINT `vehic
les_user_id_foreign` FOREIGN KEY (`user_id`) REFERENCES `app`.`users` (`id`
))
I looked up what this error is supposed to mean, and also found examples of other people running into the same problem, even just related to using MySQL, and their solutions, but applying:
DB::statement('SET FOREIGN_KEY_CHECKS=0;'); and
DB::statement('SET FOREIGN_KEY_CHECKS=1;');
Within down() doesn't seem to work and when I run describe in MySQL the tables look right.
The migrations are named properly to make sure the users table is migrated first, and then vehicles so the foreign key can be applied, and the tables being setup up correctly suggests the migrations were run, but then the error occurs. I dropped and recreated the DB and tried it again and it is the same result. I also don't understand why it is trying to truncate on the first migration and seed of the database, I wouldn't have thought that would occur when you tried to run php artisan migrate:refresh --seed.
// 2015_06_17_100000_create_users_table.php
class CreateUsersTable extends Migration
{
public function up()
{
Schema::create('users', function (Blueprint $table) {
$table->increments('id');
$table->string('username', 60)->unique();
$table->string('email', 200)->unique();
$table->string('password', 255);
$table->string('role')->default('user');
$table->rememberToken();
$table->timestamps();
});
}
}
public function down()
{
Schema::drop('users');
}
// 2015_06_17_300000_create_vehicles_table.php
class CreateVehiclesTable extends Migration
{
public function up()
{
Schema::create('vehicles', function (Blueprint $table) {
$table->increments('id');
$table->integer('user_id')->unsigned();
$table->string('make');
$table->string('model');
$table->string('year');
$table->string('color');
$table->string('plate');
$table->timestamps();
$table->foreign('user_id')->references('id')->on('users');
});
}
}
public function down()
{
Schema::drop('vehicles');
}

Answer 1

DB::statement('SET FOREIGN_KEY_CHECKS=0;');
App\User::truncate();
DB::statement('SET FOREIGN_KEY_CHECKS=1;');
And it works！

Answer 2

As the error says, you can not truncate tables referenced by foreign keys. Delete should work though...
DB::table('some_table')->delete();

Answer 3

before drop
Schema::disableForeignKeyConstraints();
and before close run method
Schema::enableForeignKeyConstraints();

Answer 4

To clear a table using Eloquent:
Model::query()->delete();
Example using default user model
User::query()->delete();

Answer 5

I faced the same issue with my Role and Permission setup and this is what I did that worked as I wanted. Truncate() will reset the Increment column to 1 but throw a foreign key error while delete on the other hand works fine but doesn't reset the increment column, so I did the following in my Seeder's file (i.e RoleSeeder.php in my case)
1. [ delete() method ]
$roles = [];
... // Some foreach statement to prepare an array of data for DB insert()
// Delete and Reset Table
DB::table('roles')->delete();
DB::statement("ALTER TABLE `roles` AUTO_INCREMENT = 1");
// Insert into table
DB::table('roles')->insert($roles);
This will cascade all other child tables attached to the roles table. in my case users_roles table. This way I avoided disabling and enabling foreign key checks.
2. Something to put in mind / Second Approach [ truncate() method ]
if you don't have the intention of deleting all the data stored in the child's table (in my case users_roles table) ... You can go with truncate() and then in the DatabaseSeeders.php file you disable and enable foreign key check. As I tested this and the users_roles data was intact, the seed on affected roles table.
//RoleSeeders.php File
$roles = [];
... // Some foreach statement to prepare an array of data for DB insert()
// Truncate Table
DB::table('roles')->truncate();
// Insert into table
DB::table('roles')->insert($roles);
Then in the DatabaseSeeder.php file, you do;
public function run()
{
DB::statement('SET FOREIGN_KEY_CHECKS=0;');
$this->call([
RoleSeeder::class,
]);
DB::statement('SET FOREIGN_KEY_CHECKS=1;');
}
But I prefer the delete() method, since I don't have to disable/enable the foreign key check

Answer 6

you can use
DB::table('your_table_name')->delete();
to empty a table, this won't delete the table structure. But the auto increment id will not start from initial number.

Answer 7

Here is what works for me every time.
When you're adding the foreign key, make sure to add cascade.
the syntax is like this
$table->foreign('column')->references('id')->on('table_name')->onDelete('cascade');
Make sure to replace id with whatever field is applicable for you.
Now before running the seeding add this instead of trucate
DB::statement('DELETE FROM table_name');
It will delete all the data.
Hope this helps.

Answer 8

You could just drop it with.
$table->dropForeign('posts_user_id_foreign');

Answer 9

I'm using Laravel 7.x, this worked for me. Goes without saying that it should only be used in development. To read more, check it out here.
DatabaseSeeder.php
<?php
use Illuminate\Database\Seeder;
class DatabaseSeeder extends Seeder
{
/**
* Seed the application's database.
*
* #return void
*/
public function run()
{
// the Eloquent part and disabling and enabling of foreign keys is only intended for development
Eloquent::unguard();
//disable foreign key check for this connection before running seeders
DB::statement('SET FOREIGN_KEY_CHECKS=0;');
$this->call(RolesTableSeeder::class);
$this->call(UsersTableSeeder::class);
// supposed to only apply to a single connection and reset it's self
// but I like to explicitly undo what I've done for clarity
DB::statement('SET FOREIGN_KEY_CHECKS=1;');
}
}