Re: [Chicken-users] DBI

[Alaric Snell-Pym]

> dbi:query-fold, dbi:query-map, query-for-each.  I thought about
> implementing these, but I
>         haven't been able to think of the use case that makes them
> necessary in the presence
>         Scheme's fold, map, and for-each, other than as shorthand (which
> could be define'd
>         in place in a heartbeat for anyone who wants it)

Result streaming. You want to avoid having a query function that
returns a list of rows, where possible, because some DB APIs will let
you stream rows from the server as you consume them.

For a million row result, being able to stream them from the server
into a function that converts them to HTML and streams them out to a
browser, or whatever, is a big save in server memory :-)

Ideally, have your query function return a proper *stream* of conses
with promises in, then use existing stream fold/map/filter on them,
of course. Vague memory there's an SRFI for that, but I've never had
the need to look it up in detail.

> dbi:insert-id  Should this come from a function, or should it be
> returned as a response to
>         dbi:query?  I wouldn't mind seeing the query handler be smart
> enough that if my query
>         involves INSERT and i've inserted a row that becomes ID 42, that
> the response would
>         be something like '((rows-affected 1) (insert-id 42)) Certainly,
> we'd want to look at what
>         we'd want to normalize these labels to, but that's not a huge issue.
>
>         The related question is whether singleton response values (like
> rows-affected with
>         nothing else) should return as a singleton (a)list or as a numeric
> value --> My vote would
>         be to return the singleton (a)list  to simplify the conditional
> checking the caller needs
>         to use.

In my past I've preferred to have "query" procedures for SQL queries,
and "execute" procedures for INSERT et al, which don't return a
table, just success/failure. Then you can have a more specific
procedure for "insert" that returns inserted ID metadata.

ABS

--
Alaric Snell-Pym
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