How to validate in detail-oracle block that atleast one record is entered?

Sometimes we have to put validation that based on some condition in master block the detail block should have at least one record or zero records.
To apply this validation ,we should first create a total_count number field in detail block.This field is the non-database summarized item calculating the total number of records in detail block.

In the key-commit we will write the following code to validate our condition:-

go_block('master-block');

if :master-block.chk_item_in_detail_blk='T' then
if :detail-block.total_count=0 then
message('Enter at least one item in detail block');
raise form_trigger_failure;
end if;
end if;