Book Image

PostgreSQL Server Programming

Book Image

PostgreSQL Server Programming

Overview of this book

Learn how to work with PostgreSQL as if you spent the last decade working on it. PostgreSQL is capable of providing you with all of the options that you have in your favourite development language and then extending that right on to the database server. With this knowledge in hand, you will be able to respond to the current demand for advanced PostgreSQL skills in a lucrative and booming market."PostgreSQL Server Programming" will show you that PostgreSQL is so much more than a database server. In fact, it could even be seen as an application development framework, with the added bonuses of transaction support, massive data storage, journaling, recovery and a host of other features that the PostgreSQL engine provides. This book will take you from learning the basic parts of a PostgreSQL function, then writing them in languages other than the built-in PL/PgSQL. You will see how to create libraries of useful code, group them into even more useful components, and distribute them to the community. You will see how to extract data from a multitude of foreign data sources, and then extend PostgreSQL to do it natively. And you can do all of this in a nifty debugging interface that will allow you to do it efficiently and with reliability.
Table of Contents (17 chapters)
PostgreSQL Server Programming
Credits
About the Authors
About the Reviewer
www.PacktPub.com
Preface
Index

Disallowing DELETE


What if our business requirements are such that data can only be added and modified in some tables, but not deleted?

One way to handle this would be to just revoke the DELETE right on these tables from all users (remember to also revoke DELETE from PUBLIC), but this can also be achieved using triggers.

A generic cancel trigger can be written as follows:

CREATE OR REPLACE FUNCTION cancel_op() 
  RETURNS TRIGGER AS $$ 
BEGIN 
    IF TG_WHEN = 'AFTER' THEN 
        RAISE EXCEPTION 'YOU ARE NOT ALLOWED TO % ROWS IN %.%', 
                          TG_OP, TG_TABLE_SCHEMA, TG_TABLE_NAME; 
    END IF; 
    RAISE NOTICE '% ON ROWS IN %.% WON''T HAPPEN', 
                          TG_OP, TG_TABLE_SCHEMA, TG_TABLE_NAME; 
    RETURN NULL; 
END; 
$$ LANGUAGE plpgsql; 

The same trigger function can be used for both BEFORE and AFTER triggers. If you use it as a BEFORE trigger the operation is skipped with a message, but if used as an AFTER trigger, an ERROR is raised and the current (sub...