Apex 4 => Apex 5 / Oracle 12c
This is a heads up post for anybody porting from Apex 4 to Apex 5 where your Apex 4 application references more than one schema.
In Apex 4, any Automatic Row Fetch or Automatic Row Processing process (and MRF/MRU) allowed the developer to select the table owner if the owner was not the default application parsing schema.
This option has been removed in Apex 5, an application can only reference the parsing schema associated with the application in ARF or ARP processes. You can still associate multiple schemas with your workspace. Your application will migrate from Apex 4 to Apex 5 OK but the table owner will be set to #OWNER# in your ARF or ARP processes (which is the application parsing schemas not the original table owner). If you have an application that updates tables from more than one schema (e.g. schemas created for different business, functional or operational areas), then this can be an issue.
This functionality is documented in the Apex 5 documentation (ie that only one parsing schema can be associated with an application). However, as far as I can see, this change in not documented in the Apex 5 release notes (Changed Behaviour, Deprecated Features, or Desupported Features), so it can catch you out.
Workarounds. You can either:-
a) Replace your ARF or ARP processes with your own packaged processes that retrieve data from another schema on page load (by using fully qualified names in your PL/SQL package process) and populate the page items; plus suitable update/delete/insert processs for the relevant buttons (in essence replicating the ARF/ARP functionality).
b) Create a solution in the database at the parsing schema level by creating synonyms/links/grants etc.
c) Consider using VPDs (if your using EE)
If this is something that you would like to see changed, have a look at Features Requests:-
https://apex.oracle.com/pls/apex/f?p=55447:19:21316197012948::NO:19:P19_ID:79869155155479471027208829146596413101