Need Master-Detail relation to link Master column to 2 different detail col

Question

I have a form with a master detail relation. The master block is a database table rec_shipments with a primary key of shipment_id and a bunch of other columns. The detail block is a table rec_containers with a container_id as the primary key plus column shipment_id, split_shipment_id, weight, volume, etc. The shipment_id and split_shipment_id are nullable.
When a shipment is received a shipment record is created and container records are created with the shipment_id populated and the split_shipment_id null. In the form a relation was created between the shipment block and the container block as shipment_id=shipment_id. This works fine. However, they have the ability to spit the original containers into smaller more manageable containers for distribution. For example if they receive a railroad car full of pallets of printer paper they may take and divide them, half into 1 rolloff bin and half into another rolloff bin. The rolloff bins will get a unique container_id for tracking. The record in the system created in the rec_containers table will have the split_shipment_id populated and the shipment_id null. In the screen they want to see the original containers (railroad car) and the split containers (rolloff bins) when the query the shipment.
What they want:
Shipment_id -- and additional information
Railroad Car ID plus additional information
Rolloff Bin 1 ID plus additional information
Rolloff Bin 2 ID plus additional information
My problem is the rolloff bins don't show up with the current relation because the shipment_id is null in the 2 rolloff bin records.
I've tried creating a view on the rec_containers table that is all the columns in the table plus 1 additional column that is
nvl(shipment_id,split_shipment_id) comp_ship_id
and set the relation to shipment_id=comp_shipment_id. I set the comp_shipment_id column to query yes and insert & update to no because I don't want to update that column in the view.
The problem is I can't update any columns, I get a can't reserve record for update or delete error.
Does anyone have any ideas how I can get the containers block to query all records where the shipment_id or split_shipment_id matches the shipment block shipment_id and still be able to update the records?
Thanks for any help.

Answer 1

Your idea of using a view is the best approach. In order to make the block updateable, you have to sst the property "Query only" for your derived item to "Yes". Witn this, the column will not be included in any further dml. About the locking... it may be that forms isn't anymore able to do proper locking when a block is based on a view. In that case, put an ON-LOCK-trigger on the block and lock the record by yourself doing y SELECT FOR UPDATE NOWAIT on the record. To just try if this would work you use a NULL in the ON-LOCK just to xheck if the dml-operations itself will work. if your view is based on only one table you have good chances that there is nothing to change, if you get an error like "View not updateable", you have to do some further adjustments
-Set the key-Mode for the block to "Non-updateable"
-Set the property "Primary key" to "Yes" for the pk-item in your block.
hope this helps