Re: [Haskelldb-users] Resend: patch for review - SQL functions and parameters

[Bjorn B. <bj...@br...>]

On Fri, Apr 4, 2008 at 5:51 PM, Justin Bailey <jgb...@gm...> wrote:
> On Fri, Apr 4, 2008 at 8:28 AM, Bjorn Bringert <bj...@br...> wrote:
>  >  this looks great. How do you substitute in values for parameters in queries?
>
>  That's something I didn't look at, but is needed. Since I'm using
>  haskelldb just to generate SQL I haven't concentrated on the runtime
>  side.  However, see below ..
>
>
>  >  Here, prepare and queryBind are something along these lines (but more
>  >  general to support multiple arguments, and with some type class
>  >  constraints):
>  >
>  >  prepare :: Database -> (a -> Query (Rel b)) -> PreparedQuery (a -> Rel b)
>  >
>  >  queryBind :: Database -> PreparedQuery (a -> Rel b) -> a -> IO [b]
>
>  I like this, and I wonder if Peter's code (mentioned in another
>  thread) addresses it. I'd be glad to take a shot at unifying the two
>  approaches, once his patch is in.
>
>  In any case, do you think the parameters should show up in the type of
>  Query (Rel b)? Any ideas how that could look, and how to make sure
>  queries can still be rendered to SQL w/o runtime values (so I can
>  still get my SQL w/o having to execute it)?

Hmm, I'm not sure that the Query should have the parameters in it,
since a Query is different from a PreparedQuery.

To render a parametrized query as SQL, you could have a function
(needs a better name):

showParamSql :: (a -> Query (Rel b)) -> String

This would have to invent names for the parameters, so it needs some
trickery inside. Or maybe, forcing you to supply a name for each
parameter:

showParamSql :: (a -> Query (Rel b)) -> String -> String

(All of the above needs to be extended with type-trickery to handle
multiple parameters)

/Björn