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

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))
          (lambda (dbsys)
            (unless qtext
              (set! qtext (file->string file)))

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?


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)
         (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.


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