Apex - General - Form Regions

When you create a Form region, Apex creates page items for all columns of the table it is based on.
All "not null" columns are automatically set to Validation -> Value Required.
So far so good.

Afterwards, you could set a "not null" item to be displayed as e.g. a Text Field (instead of Display Only), set it to Validation -> NOT Value Required, and make it read-only somehow, e.g. using some JavaScript.
You may want to do this if the column is filled by the database anyway (e.g. by an insert trigger), and you don't want to render the item as Display Only (which tends to make it look different from other disabled item types).

As you may have guessed, the (Form) Region -> Synchronize Page Items option could then cause an issue here.
It will reset the item to Validation -> Value Required, which will cause an "ITEM must have some value" error when saving the new row.

If you know which items to look out for (which may be a challenge), a query like this could be useful:

select itm.application_id
      ,itm.page_id
      ,'Item ' || itm.item_name || ' should not be Required' as issue
  from apex_application_page_items itm
  join apex_application_page_regions reg on reg.region_id = itm.region_id
  join user_tab_columns tc on (tc.table_name = reg.table_name and tc.column_name = itm.item_source)
 where itm.application_id = 25384
   and itm.is_required <> 'No'
   and reg.source_type_code = 'NATIVE_FORM'
   and reg.location_code = 'LOCAL'
   and reg.query_type_code = 'TABLE'
   and tc.nullable = 'N'

Of course the safest option would be to just render the page item as Display Only, and ignore the fact it is a bit ugly :-)

Note that for Interactive Grids, the Synchronize Columns option does a very similar thing for existing columns.
Just as dangerous as the Synchronize Page Items option, but since they both behave in the same way, maybe both are intended to be features and not bugs...

When you change a table or view that is used by a Form region, page items that are based on columns that are no longer available will become invalid.
The Apex Builder shows this in the Source -> Column section for the item, as COLUMN_NAME (Invalid), but that is not very obvious so may go unnoticed.
On the page in will show as 'ORA-00904: "COLUMN_NAME": invalid identifier', which may also go unnoticed.
You would expect this to be spotted by the Advisor, but alas.

A query like this could be useful:

with a as
 (select itm.application_id
        ,itm.page_id
        ,itm.item_name
        ,itm.item_source
        ,reg.table_owner
        ,reg.table_name
        ,(select count(*)
            from user_tab_columns tc
           where tc.table_name = reg.table_name
             and tc.column_name = itm.item_source) as view_n
    from apex_application_page_items itm
    join apex_application_page_regions reg on reg.region_id = itm.region_id
   where itm.application_id = 25384
     and itm.item_source_type = 'Region Source Column'
     and reg.source_type_code = 'NATIVE_FORM'
     and reg.location_code = 'LOCAL'
     and reg.query_type_code = 'TABLE'
  )
select a.*
  from a
 where a.view_n = 0
 order by a.application_id
         ,a.page_id
         ,a.item_name

Synchronize Page Items

ORA-00904: invalid identifier