Re: Foreign key referencing subclasses.

Hi Johannes,

On Thursday, 22. March 2001 15:18, Johannes Grødem wrote:
> Hi,
>
> it seems I can't have a foreign key that references some subclass. 
> Postgres says it can't figure out what its primary key is.  The
> primary key is defined in the superclass.
>
> I have something like this:
>
> CREATE TABLE resource_record(
>   rrid SERIAL
>   -- etc.
> );

There is no primary key for this table. Just write PRIMARY KEY after 
SERIAL.

> CREATE TABLE soa_record(
>   -- blah, blah
> ) INHERITS(resource_record);
>
> CREATE TABLE domain(
>   -- ...
>   soaid REFERENCES soa_record  -- *
> );
>
>
> * = This doesn't work. I can reference resource_record here, but I
> can not reference soa_record that way. Referencing resource_record*
> doesn't work either.

Primary keys as well as other indexes are not inherited, unfortunately. 
You should create the indexes for any subclass manually, like:

CREATE INDEX soa_record_pkey ON soa_record ( rrid );

You could also state the referenced field name (you actually have to, 
if you happen to reference to a non-primary key field):

CREATE TABLE ...soaid  int4  REFERENCES soa_record ( rrid )       ^^^^
Note that SERIAL is actually int4 with automagically created sequences.
You can't leave out the column's type for references.

And note also that referencing to a superclass* (including subclasses) 
does not work for 7.0.x. I think it changes with 7.1 but I'm not sure.
You could create your own triggers, though.

Hope that helps,

Christof.
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