Error: 1826 Duplicate foreign key constraint name 'id'

Question

I've created a basic database structured as follows.

vehicle_makes (id, name, slug)
vehicle_models (id, name, slug, make_id)
vehicle_trims (id, name, slug, model_id)

When attempting to create the vehicle_trims table via Laravel migrations, I get an error about duplicate foreign key constraint.

SQLSTATE[HY000]: General error: 1826 Duplicate foreign key constraint name 'id' (Connection: mysql, SQL: alter table `vehicle_trims` add constraint `id` foreign key (`model_id`) references `vehicle_models` (`id`) on delete cascade on update cascade)

After reading similar posts from other users here, I understand that the FK name has to be unique, but this error seems to be related to each table having a standard 'id' column.

Does that mean tables needs a unique ID such as make_id, model_id, etc. to use foreign keys, and then reference these with fk_make_id, fk_model_id and so on instead?

Migrations

vehicle_makes

<?php

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

return new class extends Migration
{
    public function up(): void
    {
        Schema::create('vehicle_makes', function (Blueprint $table) {
            $table->id();
            
            $table->string('name');
            $table->string('slug');
            
            $table->timestamps();
        });
    }

    public function down(): void
    {
        Schema::dropIfExists('vehicle_makes');
    }
};

vehicle_models

<?php

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

return new class extends Migration
{
    public function up(): void
    {
        Schema::create('vehicle_models', function (Blueprint $table) {
            $table->id();
            
            $table->string('name');
            $table->string('slug');
            
            $table->foreignId('make_id')
                ->constrained(table: 'vehicle_makes', indexName: 'id')
                ->onUpdate('cascade')
                ->onDelete('cascade');
            
            $table->timestamps();
        });
    }

    public function down(): void
    {
        Schema::dropIfExists('vehicle_models');
    }
};

vehicle_trims

<?php

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

return new class extends Migration
{
    public function up(): void
    {
        Schema::create('vehicle_trims', function (Blueprint $table) {
            $table->id();
            
            $table->string('name');
            $table->string('slug');
            $table->year('year');
            
            $table->foreignId('model_id')
                ->constrained(table: 'vehicle_models', indexName: 'id')
                ->onUpdate('cascade')
                ->onDelete('cascade');
            
            $table->timestamps();
        });
    }

    public function down(): void
    {
        Schema::dropIfExists('vehicle_trims');
    }
};

Answer 1

->constrained(table: 'vehicle_models', indexName: 'id')

indexName here is the name for the index, not the column, so it has to be unique e.g vehicle_trims_model_id, but you can omit it completely and Laravel will use a default convention for indexes naming.

If you had a differently named key in foreign table than 'id' you could use

$table->foreign('model_id')->references('not_conventional_id')->on('vehicle_models');

https://laravel.com/docs/11.x/migrations#foreign-key-constraints