Re: [Chicken-users] A call to arms

[Alaric Snell-Pym]

On 22 Jan 2009, at 8:27 pm, Peter Bex wrote:

> On Thu, Jan 22, 2009 at 03:01:30PM -0500, Andrew Gwozdziewycz wrote:
> > So, if you have to simulate features of the storage engine to get
> > compatibility, all you have to do is tell users that there are some
> > limitations
> > to it. Give them the information to choose for themselves. But, on
> > the
> > other hand, if they end up growing significantly, and decide to
> > switch
> > storage engines from ASCII files to Postgres, why should they have
> > to do
> > any more than recompile/restart with a different connection
> > parameter?
>
> Because if you provide the same abstract interface to all the storage
> engines, you won't be able to leverage any of them to their fullest
> extent.  You'll always end up either abstracting away too many
> essential
> details, or provide a way around the abstraction, in which case it
> isn't
> complete anymore.

All of this is why I decided Wings should sit above this - all it
cares about is getters and setters. If you get those getters and
setters from an OR mapping engine, or something that just wraps SQL
queries:

(define-sql-row flight-cost (id cost))

(make-sql-getter *db-connection* flight-costs "SELECT id,cost FROM
flights WHERE cost < [[cost]] AND destination = [[destination]]")
-> #<procedure (? cost destination)>

Call that function on a cost and destination, and get back a list of
flight-cost records (define-sql-row is much like define-record, except
it makes a constructor that works from an SQL result)

(define-sql-row flight-details (id cost destination))

(make-sql-record-source *db-connection* flight-details "flights" ("id"))

...by introspecting into the structure of flight-details, produces a
function that does:

SELECT id,cost,destination FROM flights WHERE id = ?

...and which has a setter that, given an id and a flight-details-
record, does:

UPDATE flights SET id=?,cost=?,destination=? WHERE id = ?

By putting the abstraction layer above the level of "how the structure
of a result is specified", we can get away with doing all sorts of
different things.

ABS

--
Alaric Snell-Pym
Work: http://www.snell-systems.co.uk/
Play: http://www.snell-pym.org.uk/alaric/
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