Question

我最近尝试使用OCaml来处理Postgres数据库。我找到了PG'Ocaml库并且坚持了第一个例子。那就是错误：

$ make
ocamlfind ocamlc -package pgocaml,pgocaml.syntax -syntax camlp4o -c test.ml
File "test.ml", line 7, characters 23-146 (end at line 12, character 2):
Camlp4: Uncaught exception: Unix.Unix_error (20 | CstTag21, "connect", "")

File "test.ml", line 1:
Error: Preprocessor error
make: *** [test.cmo] Error 2

这是某种类似的问题（https://lists.gnu.org/archive/html/modcaml/2008-05/msg00000.html），但结论对我不起作用，因为使用

进行记录

$ psql -h localhost -d adam - U adam

完全有效，我已经包含了行

let dbh = PGOCaml.connect ~host:"localhost" ~user:"adam" ~datebase:"adam"
  ~password:"******" () in

进入我的代码。

这是我的Makefile：

PROJECT := test
LINK_PKG := pgocaml
COMP_PKG := pgocaml,pgocaml.syntax

all: $(PROJECT)

$(PROJECT): $(PROJECT).cmo
    ocamlfind ocamlc -package $(LINK_PKG) -linkpkg -o $@ $<

$(PROJECT).cmo: $(PROJECT).ml
    ocamlfind ocamlc -package $(COMP_PKG) -syntax camlp4o -c $<

这就是整个代码：

open Printf

let () =
  let dbh = PGOCaml.connect ~host:"localhost" ~user:"adam" ~datebase:"adam"
  ~password:"******" () in

  PGSQL(dbh) "execute" "create temporary table employees (
id serial not null primary key,
name text not null,
salary int4 not null,
email text
)";

  let insert =
    PGPREPARE(dbh) "opt-args"
    "insert into employees (name, salary, email)
values ($name, $salary, $?email)"
  in
  insert "Ann" 10_000_l ();
  insert "Bob" 45_000_l ();
  insert "Jim" 20_000_l ();
  insert ~name:"Mary" ~salary:30_000_l ~email:"mary@example.com" ();

  let rows = PGSQL(dbh) "select id, name, salary, email from employees" in
  List.iter (
    fun (id, name, salary, email) ->
      let email = match email with Some email -> email | None -> "-" in
      printf "%ld %S %ld %S\n" id name salary email
  ) rows;

  let ids = [ 1_l; 3_l ] in
  let rows = PGSQL(dbh) "select id, name, salary, email from employees
where id in $@ids" in
  List.iter (
    fun (id, name, salary, email) ->
      let email = match email with Some email -> email | None -> "-" in
      printf "%ld %S %ld %S\n" id name salary email
  ) rows;

  PGOCaml.close dbh

无法使用OCaml与PostgreSQL数据库连接

0 个答案: