package fun-postgresql

fun-sql - functional-style SQL queries for OCaml

Copyright 2022 Yawar Amin

This file is part of fun-sql.

fun-sql is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

fun-sql is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with fun- sql. If not, see https://www.gnu.org/licenses/.

What is this

A simple functional-style query runner and mapper for PostgreSQL and SQLite (MySQL support is also desired if anyone wants to contribute!).

Designed to make it easy to create prepared statements and then use them:

(* Prepared statement: *)
let edit_note = query db "update note set txt = $1 where id = $2"

(* Use by simply calling it: *)
let edit_note id txt = edit_note ~args:Arg.[int id; text txt] unit

Examples

open Fun_postgresql
(* Or: Fun_sqlite *)

(* Test DB *)
let db = new Postgresql.connection ~conninfo:"postgresql://..." ()
(* Or: let db = Sqlite3.db_open ":memory:" *)

(* DDL query with no arguments and no return *)
let () = query db "create table people (name text not null, age int)" unit

(* Insert query with single row *)
let () = query
  db
  (sql "insert into people (name, age) values (%a, %a)" placeholder 0 placeholder 1)
  ~args:Arg.[text "A"; int 1]
  unit

(* Get single column of results from DB *)
let names = query
  db
  (sql "select name from people where age = %a" placeholder 0)
  ~args:Arg.[int 1]
  @@ ret @@ text 0
(* val names : string Seq.t = <fun> *)

let () =
  query
    db
    (sql "insert into people (name) values (%a)" placeholder 0)
    ~args:Arg.[text "B"]
    unit

(* Get optional values *)
let ages = List.of_seq
  @@ query db "select age from people" @@ ret @@ opt int 0
(* val ages : int option list = [Some 1; None] *)

(* Map return data to a custom type on the fly *)
type person = { name : string; age : int option }

let person row = { name = text 0 row; age = opt int 1 row }
(* val person : row -> person *)

(* Assert resultset has a single row and map it *)
let person_1 = only
  @@ query db (sql "select name, age from people where age = %a" placeholder 0) ~args:Arg.[int 1]
  @@ ret person
(* val person_1 : person = {name = "A"; age = Some 1} *)

(* Assert resultset has either 0 or 1 element *)
let opt_person_1 = optional
  @@ query db (sql "select name, age from people where age = %a" placeholder 0) ~args:Arg.[int 2]
  @@ ret person
(* val opt_person_1 : person option = None *)

(* Batch insert *)

let ppl = [{ name = "B"; age = None }; { name = "C"; age = Some 3 }]

let () = batch_insert
  db
  (sql "insert into people (name, age) values (%a, %a)" placeholder 0 placeholder 1)
  ppl
  (fun { name; age } -> Arg.[text name; opt int age])
  unit