Update field on new post?

[Kaitlyn2004]

I added a field to the post table and in hook postdata_save, I have (trimmed down for display):

$this->validfields['myfield'] = array(TYPE_INT, REQ_NO);
$this->set('myfield', 1);

This works just fine, HOWEVER it doesn't work on a new thread post (first post).

It looks like there is threadfpdata_presave but if I do the same thing, it wants to add that field to the thread. I don't have any fields in the thread table or want to alter it, so how do I accomplish this?

thanks!