Use with ocaml-mariadb

[Kingdutch]

I use Mariadb as backend so I thought I'd use ocaml-mariadb instead of ocaml-mysql as transport. The following code almost works (in the sense that it nearly builds, haven't actually run it yet) but I have a few questions.

include Ppx_mysql_runtime.Make_context({
  module IO = Lwt;

  module Prepared = {
    type dbh = Mariadb_with_lwt.t;

    type stmt = Mariadb_with_lwt.Stmt.t;

    type stmt_result = Mariadb_with_lwt.Res.t;

    type error = Mariadb_with_lwt.error;

    let wrap = (f, x) =>
      Lwt.Infix.(
        Lwt.catch(
          () => Lwt_preemptive.detach(f, x) >>= (v => Lwt.return_ok(v)),
          exn => Lwt.return_error(exn),
        )
      );

    let create = Mariadb_with_lwt.prepare;

    let close = Mariadb_with_lwt.Stmt.close;

    let execute_null = (stmt, args) =>
      wrap(Mariadb_with_lwt.Stmt.execute(stmt), args);

    let fetch = Mariadb_with_lwt.Res.fetch;
  };
});

1. The execute_null function takes a string option array, however from what I can tell ocaml-mariadb takes Field.t instances. I could write a small wrapper here but I'm not sure how to get type information out of the string option array passed to execute_null to map it to what ocaml-mariadb expects.

2. I'm unsure what the wrap function needs. The Mariadb_with_lwt is the lwt nonblocking implementation of ocaml-mariadb taken straight from their examples (mariadb_with_lwt.re). It appears that the type signatures are already result based so they don't need the exn -> result wrapping that is used for ocaml-mysql.

3. Possibly should be a separate issue but how would I use connection pooling? Would it beat all needed? I don't think either ocaml-mariadb or ocaml-mysql seems to support it? Does ppx_mysql have anything special for it?