[Dbix-class] Optimistic locking

[David Wheeler]

On Aug 4, 2006, at 10:07, Dan Horne wrote:

> So, my question is: Is there any way to create such a pseudocolumn  
> that can
> be populated as a result of the values of the other columns?

If you want to use a real column, you can add it to your table and  
then add a trigger to the table to compute the hash. Something like  
this (in PostgreSQL):

CREATE OR REPLACE FUNCTION hash_row() RETURNS trigger AS $$
   NEW.hash = md5(NEW.foo || NEW.bar || NEW.baz);
   RETURN NEW;
$$ LANGUAGE sql;

CREATE TRIGGER hash_row BEFORE UPDATE OR INSERT ON mytable
FOR EACH ROW EXECUTE PROCEDURE hash_row();

Best,

David