保存新的1：n关系

I have a record header with a model of RecordHeader
RecordHeader (id PRIMARY KEY, entryDate DATETIME, fullName TEXT)

I have record details with a model of RecordDetails
RecordDetails (id PRIMARY KEY, headerID FOREIGN KEY, answer TEXT)

My RecordHeader has a relationship defined:

public $hasMany = array('RecordDetails' => array(
    'from' => 'RecordHeaders',
    'to' => 'RecordDetails',
    'key' => array('id' => 'headerID'),
    'fieldName' => 'details'
));

I save a view with an "id" hidden field, a "headerID" hidden field, a "fullName" text field with some arbitrary name ("xyz789"), and an "answer" text field, which I put in some arbitrary data("abc123").

My controller strips out the id and headerID if its empty, which it will be at the start of a new series of questions and fills in the entryDate

$record = RecordHeaders::create($this->request->data);
$record->save();

I have data in RecordHeaders but nothing in RecordDetails.
RecordHeader(1, "2012-03-30 12:40", "xyz789")
RecordDetails table is empty

The request does contain the "answer" of "abc123" when I inspect it on RecordHeaders::create()

Am I doing something wrong, or can I only save the RecordDetails if the RecordHeader is already in the database, and I call the save on a RecordDetails object?