How to add foreign key in existing table migration

In this tutorial we will discuss how to add foreign key column in existing table by migration. laravel add foreign key constraint migration. laravel migration droping column with foreign key constraint.

Laravel add foreign key column to existing table

Let our database have a users table which primary key id have unsigend biginteger type and there also have a products table which not have any relation with users table. Now we want to add a relation between users and products add a foreign key in products table.

Migration command

php artisan make:migration add_user_id_in_products_table --table=products

This command create a new migration

Foreign key add migration

In code we create a user_id foreign key in up() method and in down() method first remove foreign key constraint after drop that column.

<?php

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;
use App\Models\Product;

class AddUserIdProductsTable extends Migration
{

  public function up()
  {
    Schema::table('users', function($table) {
        $table->biginteger('user_id')->unsigned();
        $table->foreign('user_id')->references('id')->on('users')->onUpdate('cascade')->onDelete('cascade');
    });
  }

  // rollback the migration
  public function down()
  {
    Schema::table('users', function($table) {
        $table->dropForeign('user_id');
        $table->dropColumn('user_id');
    });
  }
}