Call to undefined method (using File_MARC library)?

Control fields in MARC don't have subfields, which is why the getSubfields() method is not defined for File_MARC_Control_Field. I don't know what your code or the Drupal code looks like, but I'm guessing it's iterating over every field in the record and blindly trying to grab subfields from them. You need to test to see if the field is an instance of File_MARC_Control_Field or File_MARC_Data_Field first before trying to grab subfields.

Thanks for replying Dan. In a way that sort of makes my day that you responded to this bug report.

You're right, the function calling getSubfields is just a very generic helper function to help mitigate the issue that File_MARC may or may not be installed and is just blindly trying to grab a subfield value.

I'm not sure how I haven't seen this myself but it looks like I was not accounting for control fields and the fix should be pretty easy. Unfortunately, I am overwhelmed at work right now and don't have time to do it immediately.

Here is the code:

function marc_value($marc, $key){
  $field = substr($key, 0, 3);
  $subfield = substr($key, 4, 1);
  if ($marc->record) {
    $record = $marc->record;
    $marcfield = $record->getField($field);
    if ($marcfield){
      $marcsubfield = $marcfield->getSubfield($subfield);
    }
    if ($marcsubfield){
      $value = $marcsubfield->getData();
    }
  }
  elseif ($marc->legacy) {
    $value = $marc->legacy[$field][0][$subfield];
  }
  if ($value){
    return $value;
  }
}

In the meantime, you could probably just hack the module if you needed an immediate fix. I am still figuring out File_MARC but I would think this might work. - Maybe Dan has a better fix? I am assuming I can getData() for a control field but I haven't tried it.

function marc_value($marc, $key){
  $field = substr($key, 0, 3);
  $subfield = substr($key, 4, 1);
  if ($marc->record) {
    $record = $marc->record;
    $marcfield = $record->getField($field);
    if ($subfield){
      if ($marcfield){
        $marcsubfield = $marcfield->getSubfield($subfield);
      }
      if ($marcsubfield){
        $value = $marcsubfield->getData();
      }
    }
    else {
      $value = $marcfield->getData();
    }
  }
  elseif ($marc->legacy) {
    $value = $marc->legacy[$field][0][$subfield];
  }
  if ($value){
    return $value;
  }
}

Heh, thank my Google Alert for bringing this to my attention :)

If I understand correctly what you're doing here, try the instanceof operator to determine whether the field you've retrieved is a data field or control field:

function marc_value($marc, $key){
  $field = substr($key, 0, 3);
  $subfield = substr($key, 4, 1);
  if ($marc->record) {
    $record = $marc->record;
    $marcfield = $record->getField($field);
    if ($marcfield instanceof File_MARC_Data_Field){
      $marcsubfield = $marcfield->getSubfield($subfield);
    }
    if ($marcsubfield){
      $value = $marcsubfield->getData();
    }
  }
  elseif ($marc->legacy) {
    $value = $marc->legacy[$field][0][$subfield];
  }
  if ($value){
    return $value;
  }
}

I'm not what you want to have happen if someone calls marc_value() with a control field tag ("008") and a subfield ("a"); you could either ignore the subfield value and just call getData() on the field, or return an error saying "don't do that!".

Oops it looks like I put: $marcfield = $record->getField($field) on the wrong side of the if, so when it tried to $marcfield->getData(), there was no $marcfield.

I fixed it above. Although, it still has not really been tested.