Trying to access transient objects in an edit screen

In the past, to access an entity in an edit screen that related to the main datasource, we have added a column to the Entity/Table containing a many-to-one associative relationship with the needed entity - then added that entity and it’s needed data to the view.
Then we would add a nested collectiondatascource with the newly attached entity and set the datasource in a lookup field to the main datasource, and add the collection datasource as the new nested one. Then we could set the property.

I’ve been asked not to alter the table this time, so I’ve added the related entity as a transient List and followed all the same steps. When I try to populate a lookup field with the List, nothing happens.

Are there different steps when working with a transient relationship?
Is there an alternate way to populate fields with two related entities in the same screen?

Solved. I needed to use Composition.