Re: foreign keys to foreign tables

Obviously the server will be able to delete those rows because it will be
completely unaware of this dependency.

So it is the implied reverse constraint (of sorts) that can't be enforced
which makes an FK based definition impossible.

For my particular use case, this shouldn't be a problem. The foreign table
is a reference table which does not typically experience deletes. I'll go
with a function for now. Since this happens to be a PostgreSQL-PostgreSQL
mapping I'll also consider mapping my table back the other way and then
putting a delete trigger on the foreign reference table to either cascade
or stop the delete once I decide which I'd rather do.

Thanks for the help!

On Mon, Jun 22, 2015 at 12:21 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Rick Otten <rottenwindfish(at)gmail(dot)com> writes:
> > Hello pgsql-general,
> > I'd like to set up a foreign key constraint to a foreign table from a
> local
> > table.
>
> > ie, I have a column in a local table that I'd like to ensure has a value
> in
> > the foreign table.
>
> > alter mytable
> > add column some_column_id uuid references
> myforeigntable(some_column_id)
> > ;
>
> > Unfortunately I get a "not a table" error when I try this.
>
> > ERROR: referenced relation "myforeigntable" is not a table
>
> > I'm thinking I'll have to write a function that checks for existance of
> the
> > ids in the foreign table, and then put a CHECK constraint on using that
> > function, but I thought I'd as first if there was a better way.
>
> What's going to happen when the foreign server decides to delete some rows
> from its table?
>
> regards, tom lane
>