In the master we have our customer info and in the detail the products he's interested in.
Oracle APEX provides a wizard to create a Master-Detail Form
You've some options for the layout - edit the records directly on the detail screen or as a separate form. Which one to pick? It depends... for small detail tables I would go for a Tabular Form, but for larger or more complex ones I would go with another Form. Tabular Forms are not the most flexible in APEX, but for now that is the only declarative option you have to edit multiple records at the same time. Alternatives are to use Modal dialogs, code your own custom solution or use a solution of somebody else. FOEX for example has a nice solution which I'll cover in the next post.
Tabular forms got improved only a little bit in APEX 5.0, but Modal Dialogs come native in APEX 5.0. Tabular Forms will be more enhanced in APEX 5.1 which can then do master - detail - detail and it will also come with another solution - a new "Multi-Row Edit" region type - which could work well in this case.
You find the Master Detail result online at https://www.apexrnd.be/ords/f?p=DGIELIS_BLOG:MASTER_DETAIL
What if our tables were a bit more complex and we need Master-Detail-Detail today?
We would need to create our own custom "tabular forms", basically a report where we use the apex_item api... but that is for another post.