Duplicate check on one column in only one datablock

Question

hi all,
i have a database block with three columns.
X Y Z
X is a display item and not navigable. Y has to be a unique number therefore no duplicate number can be added before commit is done and Z is check box.
i have written a code for this in the pre-update trigger but the issue is when i update the checkbox it looks as if the Y clumn has been changed. could some please tell me a better method to check for duplicate check.
any advice would be really helpful. thanks in advance.

Answer 1

I saw your other thread asking how to prevent duplicate keys on a database.
I am not sure what code you wrote in the pre-update trigger, but it sounds like you are checking for a duplicate record in the database, but NOT excluding the present record. You can add: AND ROWID <> :this_block.ROWID
to your where clause, and it should bypass the present record when checking for a duplicate. (Change "this_block" to the name of your forms block.) Also, did you write a similar pre-insert trigger? It would be better to write the code for both insert and updates in a when-validate-record trigger (see below).
However, after saying all that, you can do all sorts of checks in your form, but none of them will trap the situation where a second user inserts or updates a record with the same key at the first user. The only thing you can do to prevent duplicates and be 100% sure is to create a unique constraint on the database table. Then you will need to write code in the form to check when the error is raised. Here is a thread where that method is discussed:
Re: Question about Unique Table Columns - How to Handle Alerts
Also, in your other thread, you asked about using a record group to prevent duplicates. You can read this thread:
Re: Hi all, Very interesting problem to tackle,..help me
Here is code for a when-validate-record trigger to check for duplicates:
Declare
  dummy varchar2(1);
Begin
  -- check if inserting OR changing key:
  If :System.record_status = 'INSERT'
  or :System.record_status = 'CHANGED'
    and :this_block.key_item
    <> get_item_property('THIS_BLOCK.KEY_ITEM',database_value) then
    begin
      Select 'X' into dummy from table where key_item = :this_block.key_item;
    exception when no_data_found then null;
    end;
    If dummy='X' then
      Message('  Record already exists on the database');
      Raise form_trigger_failure;
  End if;
End;For small tables (those with maybe less than a thousand rows) you can use the famous Kevin Clarke duplicate summary function to trap for duplicates within the block. But this method depends on your always fetching all rows into the block every time you query.
You can see a description of the method in the following threads:
Duplicate key prevention
Re: checking for same rows in a tabular
Re: duplicate records in  a multi record block