Re: arrays of foreign keys

On Fri, Sep 07, 2007 at 11:47:40PM -0000, Max wrote:
> Hello,
>
> And pardon me if I posted this question to the wrong list, it seems
> this list is the most appropriate.
>
> I am trying to create a table with an array containing foreign keys.
> I've searched through the documentation and couldn't find a way to
> do so.
>
> Is this something that one can do?

It may be, but it's a bad idea.

> Basically, I have two tables:
>
> create table user (
> user_id serial,
> login varchar(50) primary key,
> tags integer[]-- this is where the problem lies

Yes, it's a design problem.

> );
>
> create table tag (
> tag_id serial,
> name varchar(50) primary key
> );
>
> I would like the user.tags field to be a list of foreign keys (tag_ids
> specifically).
>
> I know I can solve my problem with the following table:
>
> create table user_tag (
> user_id integer,
> tag_id integer,
> foreign key (user_id) references table user(user_id) on delete
> cascade,
> foreign key (tag_id) references table tag(tag_id) on delete cascade,
> primary key (user_id,tag_id)
> );
>
> But I would really like to avoid doing that.

Why? It's good, standard, normalized design, and it will work just
fine. You can make a VIEW atop this one using array_accum(), and you
can even make that VIEW writeable if you come up with behavior for
INSERT, UPDATE and DELETE.

> Is there a solution to this problem with arrays of foreign keys, and
> if so, how does one do that?

See above :)

Cheers,
David.

>
> Thanks for any help.
>
> Max
>
>
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--
David Fetter <david(at)fetter(dot)org> http://fetter.org/
phone: +1 415 235 3778 AIM: dfetter666
Skype: davidfetter

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