How to find all object which will be dropped by CASCADE? - postgresql

Question

When I drop something:
ALTER TABLE "order_bt" DROP COLUMN "billed_to"
Documentation says that I can see what depend on billed_to column:
DETAIL: view "order" depends on column billed_to of table order_bt
But on order view there are also triggers which depend on order, which will be dropped with CASCADE
Is there an option will allow to see full list of what would be dropped by CASCADE?

Answer 1

I created an example structure to check dependencies. You can try it on your database, of course objects ID will be different.
CREATE TABLE parents (
id_parent integer NOT NULL,
name_parent varchar(100),
CONSTRAINT pk_parents_id PRIMARY KEY (id_parent)
);
CREATE TABLE childs (
id_child integer NOT NULL,
name_child varchar(100),
parent_id integer,
CONSTRAINT pk_childs_id PRIMARY KEY (id_child),
CONSTRAINT fk_childs_parent_id__parents FOREIGN KEY (parent_id)
REFERENCES parents (id_parent) MATCH SIMPLE
ON UPDATE CASCADE ON DELETE CASCADE
);
CREATE OR REPLACE VIEW public.parents_view AS
SELECT parents.id_parent,
parents.name_parent
FROM parents;
CREATE FUNCTION test_trigger() RETURNS TRIGGER AS $$
BEGIN
IF TG_OP = 'INSERT' then
raise notice 'INSERT trigger, NEW = [%]', NEW;
ELSIF TG_OP = 'UPDATE' then
raise notice 'UPDATE trigger, OLD = [%], NEW = [%]', OLD, NEW;
ELSE
raise notice 'DELETE trigger, OLD = [%]', OLD;
END IF;
RETURN NULL;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER parents_view_trigger INSTEAD OF INSERT OR UPDATE OR DELETE ON parents_view FOR EACH ROW EXECUTE PROCEDURE test_trigger();
Objects that depend of table "parents":
SELECT
refclassid, refobjid, refobjsubid,
pg_describe_object(refclassid, refobjid, refobjsubid),
--pg_identify_object (refclassid, refobjid, refobjsubid) ,
classid, objid, objsubid,
pg_describe_object(classid, objid, objsubid),
--pg_identify_object (classid, objid, objsubid) ,
pg_get_constraintdef(objid),
deptype
FROM pg_depend
WHERE refobjid IN ('parents'::regclass) -- and deptype IN ('n', 'a')
ORDER BY classid, refobjid;
Output:
refclassid
refobjid
refobjsubid
pg_describe_object refobject
classid
objid
objsubid
pg_describe_object object
pg_get_constraintdef
deptype
1259
2305241
0
table parents
1247
2305243
0
type parents
i
1259
2305241
1
table parents column id_parent
2606
2305245
0
constraint pk_parents_id on table parents
PRIMARY KEY (id_parent)
a
1259
2305241
1
table parents column id_parent
2606
2305251
0
constraint fk_childs_parent_id__parents on table childs
FOREIGN KEY (parent_id) REFERENCES parents(id_parent) ON UPDATE CASCADE ON DELETE CASCADE
n
1259
2305241
1
table parents column id_parent
2618
2305259
0
rule _RETURN on view parents_view
n
1259
2305241
2
table parents column name_parent
2618
2305259
0
rule _RETURN on view parents_view
n
Objects that depend of view "parents_view":
SELECT
refclassid, refobjid, refobjsubid,
pg_describe_object(refclassid, refobjid, refobjsubid),
--pg_identify_object (refclassid, refobjid, refobjsubid),
classid, objid, objsubid,
pg_describe_object(classid, objid, objsubid),
--pg_identify_object (classid, objid, objsubid) ,
pg_get_constraintdef(objid),
deptype
FROM pg_depend
WHERE refobjid IN ('parents_view'::regclass) -- and deptype IN ('n', 'a')
ORDER BY classid, refobjid;
Output:
refclassid
refobjid
refobjsubid
pg_describe_object refobj
classid
objid
objsubid
pg_describe_object obj
pg_get_constraintdef
deptype
1259
2305256
0
view parents_view
1247
2305258
0
type parents_view
i
1259
2305256
0
view parents_view
2618
2305259
0
rule _RETURN on view parents_view
i
1259
2305256
0
view parents_view
2618
2305259
0
rule _RETURN on view parents_view
n
1259
2305256
0
view parents_view
2620
2305260
0
trigger parents_view_trigger on view parents_view
a
You can check that view "parents_view" (object ID: 2305256) not depend of table parents but rule "rule _RETURN on view parents_view" (object ID: 2305259) does, and "trigger parents_view_trigger on view parents_view" depends on parents_view, this is the reason why recursive query do not return view dependent information.
Triggers are DEPENDENCY_AUTO type (a): The dependent object can be dropped separately from the referenced object, and should be automatically dropped (regardless of RESTRICT or CASCADE mode) if the referenced object is dropped. Example: a named constraint on a table is made auto-dependent on the table, so that it will go away if the table is dropped.
You can try a query like this, but you should try to improve it:
You can restrict the result filtering by deptype.
WITH RECURSIVE pg_depend_recursive AS (
SELECT d.refclassid, d.refobjid, d.refobjsubid, d.classid, d.objid, d.objsubid, d.deptype
FROM pg_depend d
where refobjid = 'parents'::regclass
UNION
SELECT d.refclassid, d.refobjid, d.refobjsubid, d.classid, d.objid, d.objsubid, d.deptype
FROM pg_depend d
INNER JOIN pg_depend_recursive dr ON d.refobjid = dr.objid),
pg_depend_recursive2 AS (SELECT d.refclassid, d.refobjid, d.refobjsubid, d.classid, d.objid, d.objsubid, d.deptype
FROM pg_depend_recursive d
UNION
SELECT d.refclassid, d.refobjid, d.refobjsubid, d.classid, d.objid, d.objsubid, d.deptype
FROM pg_depend d
INNER JOIN pg_depend_recursive2 dr ON d.objid = dr.objid AND pg_describe_object(dr.classid, dr.objid, dr.objsubid) ilike 'rule%'),
pg_depend_recursive3 AS (SELECT d.refclassid, d.refobjid, d.refobjsubid, d.classid, d.objid, d.objsubid, d.deptype
FROM pg_depend_recursive2 d
UNION
SELECT d.refclassid, d.refobjid, d.refobjsubid, d.classid, d.objid, d.objsubid, d.deptype
FROM pg_depend d
INNER JOIN pg_depend_recursive3 dr ON d.refobjid = dr.refobjid)
SELECT refclassid, refobjid, refobjsubid, pg_describe_object(refclassid, refobjid, refobjsubid),
classid, objid, objsubid, pg_describe_object(classid, objid, objsubid),
deptype
FROM pg_depend_recursive3;