Handle CONSTRAINT TRIGGER on DB Manager/PostgreSQL.

[espinafre]

Fixes #35967

Despite appearing as constraints on the catalog pg_constraint, they are not really constraints, but rather a special kind of trigger, as seen here: https://www.postgresql.org/docs/12/catalog-pg-constraint.html and here: https://www.postgresql.org/docs/12/sql-createtrigger.html .

The following table/trigger shows the issue:

CREATE FUNCTION hi_trigger() RETURNS TRIGGER AS $$ BEGIN RAISE NOTICE 'Hello world'; RETURN NEW; END; $$ LANGUAGE plpgsql;
CREATE TABLE test_trigger(id SERIAL NOT NULL PRIMARY KEY, value varchar(32));
CREATE CONSTRAINT TRIGGER tg_test AFTER INSERT ON test_trigger DEFERRABLE INITIALLY DEFERRED FOR EACH ROW EXECUTE PROCEDURE hi_trigger();

All the other constraint types that might appear on the catalog pg_constraint according to the PostgreSQL documentation are handled by DB Manager:

QGIS/python/plugins/db_manager/db_plugins/plugin.py

Line 1284 in 2e7bebc

types = {"c": TypeCheck, "f": TypeForeignKey, "p": TypePrimaryKey, "u": TypeUnique, "x": TypeExclusion}

Those are SQL standard, the CONSTRAINT TRIGGER is a PostgreSQL extension (according to the PostgreSQL docs), and I think it is not really a constraint in the traditional sense.

I believe this should be backported to 3.12 and 3.10.

[espinafre]

@gioman , all green. Does it look good to you?

[gioman]

@gioman , all green. Does it look good to you?

I'm not a reviewer. A dev will do it.

[espinafre]

@gioman , all green. Does it look good to you?

I'm not a reviewer. A dev will do it.

Oh, I thought you were, sorry. Maybe @m-kuhn could take a look at this, since I've recently pestered him about another PR?

[gioman]

@espinafre is this PR safe also when using old PostgreSQL releases like 9.6?

[m-kuhn]

@gioman it should be safe, but a test of current master before merging the backport would be appreciated. Please note that the 3.10 backport has been frozen for a dev cycle to have time to deal with potential issues before merging.

[gioman]

it should be safe, but a test of current master before merging the backport would be appreciated

@m-kuhn sure. Master in the nightly repo for Ubuntu bionic is stuck at code revision from 16 days ago, any idea why? At home with a tiny laptop compiling is not really an option.

[m-kuhn]

Maybe @jef-n knows more?

[jef-n]

Maybe @jef-n knows more?

the addition of qgis_process broke the packaging process - fixed in 8ee4d05 - the current build should complete (http://qgis2.qgis.org:1080/cgi-bin/build.sh)

[gioman]

the addition of qgis_process broke the packaging process - fixed in 8ee4d05 - the current build should complete (http://qgis2.qgis.org:1080/cgi-bin/build.sh)

@jef-n thanks!