On 7/31/2017 10:46 PM, Alex Harsanyi wrote:
I'm trying to write a function to keep the SQL query text outside of the
Racket source code, as this would make it easier to write and test the SQL
code.
Instead of writing:
(define query (virtual-statement (lambda (dbsys) "select ...")))
I would like to put the "select ..." part in a separate file and write
something like:
(define query (sql-query "./some-file.sql"))
The "sql-query" definition would look like this:
#lang racket
(require racket/runtime-path)
(define (sql-query file-name)
(define-runtime-path rp file-name)
(let ((qtext #f))
(virtual-statement
(lambda (dbsys)
(unless qtext
(set! qtext (file->string file)))
qtext))))
Unfortunately, `define-runtime-path` can only be used at top-level, so the
above code does not compile. It works fine without the `define-runtime-path',
I need to use it so they query files are found when the application is
compiled to a stand-alone executable.
Does anyone have an idea on how `sql-query` might be defined?
Thanks,
Alex.
Hmm. A change to a query often also means a change to its arguments
and/or its result columns, so I don't see that there is much utility in
keeping the query strings separate from the program. I certainly do
test/debug my queries first using a SQL command line, but once they are
working as I expect, I embed them into my application. I have a macro
that allows me to write [nicely formatted] free-form SQL which gets
converted into a query string suitable for use with the db library.
That said, if you really want to keep your SQL separate, I would not try
to load query strings at the point of use. Instead I would load all the
query strings at startup and store them in a hash table with appropriate
identifiers. Then the query function could [minimally] be something like:
(define queryhash (hash))
:
(define (sql-query qident . args)
(let ((dbc ...)
(qtext (hashref queryhash qident #f))
(if (and (connection? dbc)
qtext)
(apply query dbc qtext args)
(error ... )
)))
Beware that I made this up on the spot - it is only intended to
illustrate the way I would approach the problem.
YMMV,
George
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