ON DELETE CASCADE on pg_class in PostgreSQL does not work I added a foreign key on my table which references pg_class.

ALTER TABLE summary_table 
ADD FOREIGN KEY (table_oid_column) REFERENCES pg_class (oid) ON DELETE CASCADE;


I have a summary table which I keep some information about tables with their relational ids. When I drop a table I want to delete automatically related row from my summary table, so I added constraint above. But in my case, when I drop a table nothing happens.

I tried it with a test table, when I delete related row from test table, it works as expected. Such as with this foreign key constraint:

ALTER TABLE summary_table 
ADD FOREIGN KEY (table_oid_column) REFERENCES test (id) ON DELETE CASCADE;


What can be the problem? Can it be related with being a catalog table(pg_class) or a hidden system column(oid)?
Constraints are only checked when you execute SQL-level DML commands such as DELETE or UPDATE.  They are not checked when you effect a system catalog data change using a DDL command such as DROP TABLE.  Those take a different code path internally, even though they end up modifying the same data.

As a consequence, you currently cannot do what you are trying to do.  In PostgreSQL 9.3, there will be event triggers, which will address the space your problem is in.