migration.php

class MigrateOrdersAndProducts extends Seeder
{
    protected $users;
    protected $orders;
 
    public function __construct() {
    
      $this->users = [];
      $this->orders = [];
    }
 
    public function run() {
      $userKey = User::count()+1; // Store the current id to build up an insert array
      $lastLegacyUser = LegacyUser::orderBy('legacy_id', 'desc')->first();
      $lastLegacyUserId = ($lastLegacyUser) ? $lastLegacyUser->legacy_id : 0;
      $orderKey = Order::count()+1;
      
      $legacyUsers = LegacyUser::where('legacy_id', '>', $lastLegacyUserId)->orderBy('legacy_user_id', 'asc')->take(1000)->get();
      
      foreach($legacyUsers as $legacyUser) {
        $this->users[] = [
          'id' => $userKey,
          'name' => $legacyUser->name,
          'legacy_id' => $legacyUser->id,
          ...
        ];
        
        foreach($legacyUser->legacyOrders as $legacyOrder) {
          $this->orders[] = [
            'id' => $orderKey,
            'user_id' => $userKey,
            'legacy_id' => $legacyUser->id,
          ]
        }
        
        $userKey++;
        $orderKey++;
      }
      
      \DB::table('users')->insert($this->users);
      \DB::table('orders')->insert($this->orders);
    }
}