blocking select

[vbmithr]

It seems to me that selecting an empty table blocks, it is possible to have an option type returned in case the table is empty or something?

Haven't looked at it enough maybe but I can't find an easy solution to avoid (lwt-)blocking on an empty table.

[mfp]

On Tue, Jul 24, 2018 at 01:39:28AM -0700, Vincent Bernardoff wrote: It seems to me that selecting an empty table blocks, it is possible to have an option type returned in case the table is empty or something? Haven't looked at it enough maybe but I can't find an easy solution to avoid (lwt-)blocking on an empty table.

Do you have a minimal test case for this? I haven't been able to reproduce it with Sqlexpr_sqlite.Make(Sqlexpr_concurrency.Id), Sqlexpr_sqlite.Make(Sqlexpr_concurrency.Lwt), nor Sqlexpr_sqlite_lwt with the following code, adapted from the example: (* ocamlfind ocamlopt -package sqlexpr,sqlexpr.ppx,lwt.ppx -o example example.ml -thread -linkpkg *) module Sqlexpr = Sqlexpr_sqlite.Make(Sqlexpr_concurrency.Lwt) module S = Sqlexpr let init_db db = S.execute db [%sqlinit "CREATE TABLE IF NOT EXISTS users( id INTEGER PRIMARY KEY, login TEXT UNIQUE, password TEXT NON NULL, name TEXT, email TEXT );"] let fold_users db f acc = S.fold db f acc [%sqlc "SELECT @s{login}, @s{password}, @s?{email} FROM users"] let insert_user db ~login ~password ?name ?email () = S.insert db [%sqlc"INSERT INTO users(login, password, name, email) VALUES(%s, %s, %s?, %s?)"] login password name email let () = Lwt_main.run @@ let db = S.open_db "example.db" in let%lwt () = init_db db in let%lwt l1 = fold_users db (fun l (login, _, _) -> Lwt.return @@ login :: l) [] in let%lwt l2 = S.select db [%sqlc "SELECT @s{login} FROM users"] in Printf.printf "%d users\n%!" @@ List.length l1; assert (l1 = []); assert (l2 = []); Lwt.return_unit let auto_init_db, check_db, auto_check_db = [%sqlcheck "sqlite"] getting: $ ./example 0 users $

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-- Mauricio Fernández