Symfony2 / PHP对象数组

I have been trying to move some legacy code into Symfony2 but have come to something which has stumped me. I have a function

public function findSeatsOnFlights($allInfo, $flights, $seatCodes)
{
}

In both the legacy and my new code, $allInfo is the same format so do not need to worry about this. In my legacy code, if I var_dump $flights and $seatCodes, I get something like

array(2) {
  [0]=> string(3) "VS7"
  [1]=> string(3) "VS8"
}
array(2) {
  [0]=> string(1) "C"
  [1]=> string(1) "D"
}

To handle this, I would do

public function findSeatsOnFlights($allInfo, $flights, $seatCodes){
    $answer = array( );

    foreach ( $flights as $flight )
    {
        $finfo = $allInfo[ $flight ];

        $fseats = $finfo["seats"];

        foreach ( $seatCodes as $code )
        {

        }
    }
}

However, with Symfony2, my var_dump of $flights and $seatCodes is

array (size=2)
  0 => 
    object(stdClass)[405]
      public '__CLASS__' => string 'Nick\AlertBundle\Entity\AvailabilityAlertFlightNumbers' (length=55)
      public 'id' => int 52
      public 'flightNumber' => string 'VS7' (length=3)
      public 'availabilityAlert' => string 'Nick\AlertBundle\Entity\AvailabilityAlert' (length=42)
  1 => 
    object(stdClass)[406]
      public '__CLASS__' => string 'Nick\AlertBundle\Entity\AvailabilityAlertFlightNumbers' (length=55)
      public 'id' => int 53
      public 'flightNumber' => string 'VS8' (length=3)
      public 'availabilityAlert' => string 'Nick\AlertBundle\Entity\AvailabilityAlert' (length=42)

array (size=2)
  0 => 
    object(stdClass)[406]
      public '__CLASS__' => string 'Nick\AlertBundle\Entity\AvailabilityAlertBookingClass' (length=54)
      public 'id' => int 62
      public 'classLetter' => string 'C' (length=1)
      public 'availabilityAlert' => string 'Nick\AlertBundle\Entity\AvailabilityAlert' (length=42)
  1 => 
    object(stdClass)[404]
      public '__CLASS__' => string 'Nick\AlertBundle\Entity\AvailabilityAlertBookingClass' (length=54)
      public 'id' => int 63
      public 'classLetter' => string 'D' (length=1)
      public 'availabilityAlert' => string 'Nick\AlertBundle\Entity\AvailabilityAlert' (length=42)

So how would I go about handling this instead? I have tried things like this without success

foreach ( $flights as $flight )
{
    $finfo = $allInfo[ $flight->getFlightNumber() ];
    ....

If I do the above I get

Warning: Illegal offset type (500 Internal Server Error)

So what is the best way of changing my code to now handle the Objects?