// database/migrations/xxxx_create_wishlists_table.php
public function up()
{
    Schema::create('wishlists', function (Blueprint $table) {
        $table->id();
        $table->foreignId('user_id')->constrained()->onDelete('cascade');
        $table->foreignId('product_id')->constrained()->onDelete('cascade');
        $table->timestamps();
        $table->unique(['user_id', 'product_id']);
    });
}