Re: Bit-wise foreign keys

On 20 Sep 2010, at 19:25, Steve Atkins wrote:
> On Sep 20, 2010, at 10:06 AM, Alban Hertroys wrote:
>> Hey all,
>>
>> I'm tossing an idea around again, namely using bit positions and values as foreign key references. Let's start with a bit of background information:
>>
>> I'm currently parsing a log-file that I want to apply all kinds of statistical analysis to. This file contains lines of records of data, among which are some bytes of which each bit marks a certain truth-value. As an internal data-object that's just dandy, but presenting it to, for example a user, or to query it for certain masks without having to delve into the definition of that particular bit-field it would be great to have a textual representation of each bit.

(...)

> Or references a single foreign value, if you have a reference table with all the valid bit combinations, which'd be pretty simple to generate programatically for small numbers of combinations.
>
> insert into foo (k integer, v text[]) values (0x21, '{"EARTH","GREEN"}';
>
> You could also apply any other set of constraints you wanted in that way (Fire is Red, Water is either Blue or Green).

(...)

I managed to find a solution that doesn't involve having n! rows for n bits, which would be a bit problematic if you ever run into 64-bit bit-fields. My solution won't function as a (foreign key) constraint though, but I didn't really need that anyway.

So far it works quite satisfactory, so I thought others might benefit from the idea. It uses standard functionality that's available in every basic Postgres installation since around 8.3 I think (I use 8.4 since a couple of days now).

Attached is what I did (you can source the below through psql).

!DSPAM:737,4ca615d7678303570290129!