I have done this in the past with other versions of SS and DOM but for some reason SS2.4.5 and most current DOM won't work for me.
I have a DataObject that has a full size image and two other thumbnails attached as $has_one relationships. IDOM is used to add the full size image and after the image upload I am presented with the usual interface to further edit the DataObject. Now in this interface I have two ImageFields to upload the two thumbnails. However when I try to attach the thumbnail images I get an error
The code line in question is $this->form->getRecord()->write();
I do now know which record getRecord() refers to here. But I assume that it is not getting the DataObject that it is supposed to attach the image to. If I look at the database I do see that the DataObject is there and is correct.
If I just hit save without attaching the thumbnails and then click on the image in IDOM I can then use the interface normally to add the thumbnails without getting the error.