Hello,
Some time ago, I developed a PostgreSQL extension to lock tuples based on
the value of a boolean attribute. If the lock is on, an exception is
raised when trying to change the row. The trigger must be disabled in
order to bypass the protection, which may not be available to a given
user.
This was done as an exercise to understand how to code a trigger in C, but
I figured out that it may be useful to some people, so I updated it and
released it as a free software.
http://people.apache.org/~fabien/tuplock/
--
Fabien