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Thread: Automaticly delete related data

Automaticly delete related data

From
Trond Arve Nordheim
Date:
Hi!

I'm developing a publishing system and are trying to create
functions/triggers that automaticly wipes out related data to the data
currently beeing deleted...

For example, I have a table containing site objects (an article or
whatever) where I have the following fields;

int_objectid SERIAL NOT NULL,
str_objecttitle VARCHAR(255) NOT NULL,
...
...

Then, I have a table defining the content of that data;
int_objectid INT(11) NOT NULL
str_data TEXT NOT NULL,
...
...

What I want to do is;
When I delete a row from the first table, I want all rows with mathing
int_objectid values in the second table to be deleted.

I've been reading in a couple of online books and the PostgreSQL
documentation all day without beeing able to make something of this...

Can anyone give me a hint, or point me in the direction of some
documentation that can help me out?

Sincerly,
Trond Arve Nordheim

Re: Automaticly delete related data

From
Stephan Szabo
Date:
On 25 Nov 2001, Trond Arve Nordheim wrote:

> Hi!
>
> I'm developing a publishing system and are trying to create
> functions/triggers that automaticly wipes out related data to the data
> currently beeing deleted...
>
> For example, I have a table containing site objects (an article or
> whatever) where I have the following fields;
>
> int_objectid SERIAL NOT NULL,
> str_objecttitle VARCHAR(255) NOT NULL,
> ...
> ...
>
> Then, I have a table defining the content of that data;
> int_objectid INT(11) NOT NULL
> str_data TEXT NOT NULL,
> ...
> ...
>
> What I want to do is;
> When I delete a row from the first table, I want all rows with mathing
> int_objectid values in the second table to be deleted.
>
> I've been reading in a couple of online books and the PostgreSQL
> documentation all day without beeing able to make something of this...
>
> Can anyone give me a hint, or point me in the direction of some
> documentation that can help me out?

If you don't mind the other semantics, you can use foreign keys
to handle this for you with the on delete cascade referential action.

Re: Automaticly delete related data

From
"Andrew G. Hammond"
Date:
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On 2001 November 24 09:10 pm, Trond Arve Nordheim wrote:

> I'm developing a publishing system and are trying to create
> functions/triggers that automaticly wipes out related data to the data
> currently beeing deleted...

This can be achieve easily using Postgres' built in referential integrity stuff.

ie:
CREATE TABLE a (id SERIAL PRIMARY KEY, title TEXT NOT NULL);
CREATE TABLE b (id SERIAL PRIMARY KEY, data TEXT NOT NULL, key_a INTEGER REFERENCES a(id) ON DELETE CASCADE);

INSERT INTO a(title) VALUES ('test');
INSERT INTO b(data, key_a) VALUES ('test data', (SELECT id FROM a WHERE title='test'));
SELECT * FROM b; -- should list one row.
DELETE FROM a;
SELECT * FROM b; -- should list no rows.

Take a look at the doc's for CREATE TABLE in the SQL reference.

- -- 
Andrew G. Hammond     mailto:drew@xyzzy.dhs.org   http://xyzzy.dhs.org/~drew/
56 2A 54 EF 19 C0 3B 43 72 69 5B E3 69 5B A1 1F                  613-389-5481
5CD3 62B0 254B DEB1 86E0  8959 093E F70A B457 84B1
"To blow recursion you must first blow recur" -- me
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