Laravel Eloquent truncate - Foreign key constraint - php

Question

I am having some issues with deleting data using Laravel 5. I seem to be stuck on a 'foreign key constraint', while I don't see why.
In my current database model I have a datapoints table, which has a foreign key to the sensors table (datapoints.sensors_id -> sensor.id).
The code I am trying:
Route::get('/truncateData', function() {
DB::table('datapoints')->truncate();
DB::table('sensors')->truncate();
return 'Done...';
});
The result:
SQLSTATE[42000]: Syntax error or access violation: 1701 Cannot
truncate a table referenced in a foreign key constraint
(alerting.datapoints, CONSTRAINT datapoints_sensor_id_foreign
FOREIGN KEY (sensor_id) REFERENCES alerting.sensors (id))
(SQL: truncate sensors)
I would understand this constraint if the order would be inverse (first deleting sensors), but when datapoints is empty, there should be no problem deleting sensors? I have also tried:
DB::table('datapoints')->delete();
DB::table('sensors')->delete();
return 'Done...';
Lastly I also tried adding explicitly 'DB::commit()' between the delete statements, but all return the same result.
Is this normal behaviour? Am I missing something?

Answer 1

No, this is the way your database works. You can't truncate table that is referenced by some other table. You may do something like
DB::statement('SET FOREIGN_KEY_CHECKS=0;');
DB::table('datapoints')->truncate();
DB::table('sensors')->truncate();
DB::statement('SET FOREIGN_KEY_CHECKS=1;');
to disable foreign key checks, truncate tables and enable it again.

Answer 2

If you prefer to use Eloquent objects, Maksym's answer the "Eloquent" way
use Illuminate\Support\Facades\Schema;
use App\Models\Datapoint;
use App\Models\Sensor;
Schema::disableForeignKeyConstraints();
Datapoint::truncate();
Sensor::truncate();
Schema::enableForeignKeyConstraints();

Answer 3

In Laravel 7 and 8, for compatibility across 4 databases (MySql, Postgres, SQLite and SqlServer) and no Eloquent, you can use:
Schema::disableForeignKeyConstraints();
DB::table('datapoints')->truncate();
DB::table('sensors')->truncate();
Schema::enableForeignKeyConstraints();