delete cascade question

[Greg Sabino Mullane]

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...
So the delete cascade states if I am deleting a row whose vname
matches the parentname delete those rows and it works fine.
...
This works, so I tried to put that in the cascade but it failed.

Not sure what you mean by "put that in the cascade." You will have
to show us your actual tables and contraints. In general, "on delete cascade"
refers to what happens to foreign key rows when the referenced key is
deleted. Similarly, you can set a constraint as "on update cascade"
in which case the changes in the parent table are also made in the child
tables. Here is a quick example that may help:

CREATE TABLE "myparent" (
"a" INTEGER,
"b" TEXT unique
);

CREATE TABLE "mychild" (
"c" INTEGER,
"d" TEXT NOT NULL
);

ALTER TABLE "mychild" ADD CONSTRAINT "mychild_d_fk"
FOREIGN KEY (d) REFERENCES myparent(b)
ON DELETE CASCADE ON UPDATE CASCADE;

INSERT INTO myparent(a,b) VALUES (1,'Garibaldi');
INSERT INTO myparent(a,b) VALUES (2,'Zathras');
INSERT INTO myparent(a,b) VALUES (3,'G''Kar');

- -- This fails, because the foreign key constraint catches the typo:
INSERT INTO mychild(c,d) VALUES (1,'Garabaldi');

INSERT INTO mychild(c,d) VALUES (9,'Garibaldi');
INSERT INTO mychild(c,d) VALUES (10,'Zathras');
INSERT INTO mychild(c,d) VALUES (11,'Zathras');

SELECT * FROM mychild;

greg=# SELECT * FROM mychild;
c | d
- ----+-----------
9 | Garibaldi
10 | Zathras
11 | Zathras


UPDATE myparent SET b = 'Chief' WHERE b='Garibaldi';

- -- ON UPDATE CASCADE has changed the name in both tables:

SELECT * FROM mychild;

c | d
- ----+---------
10 | Zathras
11 | Zathras
9 | Chief

DELETE FROM myparent WHERE b = 'Zathras';

- -- ON DELETE CASCADE has removed all the Zathras's

SELECT * FROM mychild;

c | d
- ---+-------
9 | Chief


- --
Greg Sabino Mullane ***@turnstep.com
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[Glenn MacGregor]

Sorry for being too vague. Here is my exact situation.

I have the following table currently:


Table "xpressvim"
Column | Type |
Modifiers
---------------------+------------------------+---------------------------------------------------------
vimid | integer | not null default
nextval('"xpressvim_vimid_seq"'::text)
vimname | character varying(128) | not null
vimclass | character varying(50) | not null
isadmin | boolean | not null default 'f'
adminname | character varying(136) |
vimtype | character varying(64) |
deviceconfig | character varying(64) |
deviceip | inet |
parentname | character varying(128) |
discovereditemindex | bigint |
islicensed | boolean |
addevgroupname | character varying(64) |
Primary key: xpressvim_pkey
Unique keys: xpressvim_vimname_key
Triggers: RI_ConstraintTrigger_16786,
RI_ConstraintTrigger_16788,
RI_ConstraintTrigger_16792,
RI_ConstraintTrigger_16794,
RI_ConstraintTrigger_16802,
RI_ConstraintTrigger_16804,
RI_ConstraintTrigger_16846

The constraint that I am concerned with here is the following:

CREATE CONSTRAINT TRIGGER "<unnamed>" AFTER DELETE ON "xpressvim" FROM
"xpressvim" NOT DEFERRABLE INITIALLY IMMEDIATE FOR EACH ROW EXECUTE
PROCEDURE "RI_FKey_cascade_del" ('<unnamed>', 'xpressvim', 'xpressvim',
'UNSPECIFIED', 'parentname', 'vimname');

Example data:
vimid | vimname | vimclass | isadmin | adminname | vimtype |
deviceconfig | deviceip | parentname | discovereditemindex | islicensed
| addevgroupname

1 | ***@test.com | cell | f | ***@test.com | cell | test.xml |
192.168.0.23 | | 1 | t | group1

2 | ***@test.com_if_1 | cell | f | ***@test.com | cell | test_if.xml |
192.168.0.23 | ***@test.com | 2 | t | group1

So the above constraint says if I delete row 1 (vimid = 1) then row 2
(vimid = 2) should be deleted as well because I an deleting the parent
of 2. This works fine.

Now I need to change the parentname field (in the case of vimid = 2)
from ***@test.com to test and keep the vimname field as is. When I do
this the constraint no longer works (which makes perfect sense).

1 | ***@test.com | cell | f | ***@test.com | cell | test.xml |
192.168.0.23 | | 1 | t | group1

2 | ***@test.com_if_1 | cell | f | ***@test.com | cell | test_if.xml |
192.168.0.23 | test | 2 | t | group1

delete row 1 and row 2 stays around.

Is there a way to create a constraint that will delete row 2 if I delete
row 1 using a substring of the vimname to match with the parentname?

Thanks

Glenn

Post by Greg Sabino Mullane
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Hash: SHA1

...
So the delete cascade states if I am deleting a row whose vname
matches the parentname delete those rows and it works fine.
...
This works, so I tried to put that in the cascade but it failed.

Not sure what you mean by "put that in the cascade." You will have
to show us your actual tables and contraints. In general, "on delete cascade"
refers to what happens to foreign key rows when the referenced key is
deleted. Similarly, you can set a constraint as "on update cascade"
in which case the changes in the parent table are also made in the child
CREATE TABLE "myparent" (
"a" INTEGER,
"b" TEXT unique
);
CREATE TABLE "mychild" (
"c" INTEGER,
"d" TEXT NOT NULL
);
ALTER TABLE "mychild" ADD CONSTRAINT "mychild_d_fk"
FOREIGN KEY (d) REFERENCES myparent(b)
ON DELETE CASCADE ON UPDATE CASCADE;
INSERT INTO myparent(a,b) VALUES (1,'Garibaldi');
INSERT INTO myparent(a,b) VALUES (2,'Zathras');
INSERT INTO myparent(a,b) VALUES (3,'G''Kar');
INSERT INTO mychild(c,d) VALUES (1,'Garabaldi');
INSERT INTO mychild(c,d) VALUES (9,'Garibaldi');
INSERT INTO mychild(c,d) VALUES (10,'Zathras');
INSERT INTO mychild(c,d) VALUES (11,'Zathras');
SELECT * FROM mychild;
greg=# SELECT * FROM mychild;
c | d
- ----+-----------
9 | Garibaldi
10 | Zathras
11 | Zathras
UPDATE myparent SET b = 'Chief' WHERE b='Garibaldi';
SELECT * FROM mychild;
c | d
- ----+---------
10 | Zathras
11 | Zathras
9 | Chief
DELETE FROM myparent WHERE b = 'Zathras';
- -- ON DELETE CASCADE has removed all the Zathras's
SELECT * FROM mychild;
c | d
- ---+-------
9 | Chief
- --
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[Stephan Szabo]

Post by Glenn MacGregor
Now I need to change the parentname field (in the case of vimid = 2)
this the constraint no longer works (which makes perfect sense).
192.168.0.23 | | 1 | t | group1
192.168.0.23 | test | 2 | t | group1
delete row 1 and row 2 stays around.
Is there a way to create a constraint that will delete row 2 if I delete
row 1 using a substring of the vimname to match with the parentname?

AFAIK only by writing your own trigger. You could possibly get away with
using the foreign key trigger code as a starting point.


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