Re: Conditional foreign key?

Benjamin Smith wrote:

> We have a list of customers, some of whom have purchased feature X and some of
> whom have not. If a customer has paid for featurex, they can use it, and a
> strict relationship between cust_items.items_id and items.id, but only if
> they are signed up to use featurex, otherwise I want cust_items.items_id to
> be NULL.
>
> Currently, I have tables defined similar to:
>
> create table Customer (
> id serial unique not null,
> name varchar(30) unique not null,
> FeatureX bool not null
> );
>
> Create table cust_items (
> id serial unique not null,
> customer_id integer not null references customer(id),
> name varchar(30) not null,
> type varchar not null,
> items_id integer default null references featurex(id),
> cust_active bool not null
> );
>
> // type is one of "book", "tape", or "featurex"
>
> Create table items (
> id serial not null unique,
> title varchar(30)
> );
>
>
> I want to say
> "If the cust_items.type='featurex' then (
>     (customer.featurex must be true)
>     AND
>     (cust_items.items_id must be in
>         (select id from items)
>     )";
>
> I'm just stumped as to how to say this.
>
>
> I've tried, with the above table defs,
> CREATE RULE check_customer ON UPDATE to cust_items
>     WHERE NEW.type='featurex' AND
>     NEW.customer_id IN
>         (SELECT customer.id FROM customer
>         WHERE featurex=TRUE
>         )
>     DO ... ? <too many tries to count>
>
> Any pointers, hints, or info on this kind of statement?


This is a trigger job not a rule one.


Regards
Gaetano Mendola