It would be very helpful to relative newbies to OCaml, such as myself if you had a single complete example of using Petrol. For instance, you have:

(* ... somewhere at the entry point *)
let () =
   let open Lwt_result.Syntax in
   (* ... *)
   let* conn = Caqti_lwt.connect url in
   let* () =
      Petrol.VersionedSchema.initialise
        DB.db conn in
   (* ... *)

I'm not sure what go in the line that is commented after let open Lwt_result.Syntax in or what would go after

Petrol.VersionedSchema.initialise
        DB.db conn in

in order to get a basic working example. To explain more concretely what problem I'm having in my newbie state: if I wanted to use your insert_text function after the line mentioned above, I don't know what argument I would pass to it to represent the db parameter. Would it be conn? DB.db? It would just be nice if it was made completely clear how to create a db variable that could be passed to a function like insert_text.

I realize that if I wasn't a newbie to OCaml I would probably have no issues. But I'd like to use Petrol in the course of my early learning; I'd like to be able to use a sqlite database as a starting point, and play to learn. Also, something very high-level like Petrol (compared to Caqti) seems like it would be especially advantageous to newbies. So it seems like giving newbies something that worked would make a great starting point.

Of course, you may find this training use-case to be outside the scope of what you want to do. That would be completely understandable, and I certainly wouldn't blame you in any way for simply closing this issue with no action. But, on the other hand, it doesn't seem like it would be very difficult to provide an example source file that would be a complete working example that could be run after doing opam install petrol, and it would be helpful to OCaml newbies. So, I didn't think it was completely out of line to mention it as a possibility.

Please take all this as just a friendly suggestion, with no expectations.

I did try cloning the github project and doing dune runtest, but I got all kinds of errors. This is on macos, and you mention issues with run-time loadable extensions that I'm hoping only apply when working with your project source rather than using the packaged library via opam and dune. Although I don't know that.

Thanks for listening to this particular newbie!

Inserting a boolean value into an sqlite3 database throws an exception. Removing the boolean field fixes the problem.

Error message

Fatal error: exception Failure("wrapped value list did not conform to specification - expected BOOLEAN got BOOLEAN")

Example program

open Petrol
open Petrol.Sqlite3

let db = StaticSchema.init ()

let todo, Expr.[title; desc; finished] =
  StaticSchema.declare_table db ~name:"todo"
    Schema.
      [ field "title" ~ty:Type.text
      ; field "desc" ~ty:Type.text
      ; field "finished" ~ty:Type.bool ]

let insert_todo ~title:t ~desc:d ~finished:fn db =
  Query.insert ~table:todo
    ~values:Expr.[title := s t; desc := s d; finished := bl fn]
  |> Request.make_zero |> Petrol.exec db

let test_insert =
  let open Lwt_result.Syntax in
  let* conn = Caqti_lwt.connect (Uri.of_string "sqlite3://::memory:") in
  let* _ = Petrol.StaticSchema.initialise db conn in
  insert_todo ~title:"use petrol" ~desc:"it seems amazing" ~finished:true conn

let () =
  match Lwt_main.run test_insert with
  | Ok _ ->
      print_endline "ok"
  | Error err ->
      print_endline (Caqti_error.show err)

Dune

(executable
 (name todo)
 (libraries petrol caqti-driver-sqlite3))

Setup

• petrol v1.2.0
• ocaml v5.0.0
• caqti-driver-sqlite3 v1.9.0
• sqlite3 v3.31

Caqti support more types than those expose through petrol as seen at http://paurkedal.github.io/ocaml-caqti/caqti/Caqti_type/index.html. (I'm particularly interested in timestamp, but there are few others)

Are these types possible to support in Petrol?
I wouldn't mind giving it a try but I wanted to check if there was a technical reason they are not present now, or it's just a list of things that didn't make the cut for a v1.

Would you consider / be open to dual licensing this project to also be available under a more permissive license like MIT / Apache?

I’m interested in using it (and contributed the necessary changes for #2, to make it work for my use-case), but having a less restrictive license would make it much easier for me to integrate with my existing projects 😅

Hi there, thanks for this project.
I'm personally using Core/Async and Postgres_async, I might try it but in the meantime, is it possible that Lwt specific code be well isolated within its own module?

Hello! I'm incredibly new to OCaml so if anything I've said here is completely wrong I apologize in advance.

I recently started using Petrol and was having trouble with the join alias not being applied in my project, even though it appeared that I was on the latest version (1.2.0 according to opam). I looked through the tags and it appears that there is newer versions (up to 1.2.3?) which do not show up in opam.

So I cloned and built the repo by hand to see if that fixed things and it does. It seems as though the version of Petrol being served by opam is out of date.

You may already know this, so feel free to close this issue if that's the case, I just wanted to bring it to your attention if not.

Not sure if it's a bug of me just misunderstanding how to use joins.

Assuming the following tables:

let (person, Expr.[id; name]) = StaticSchema.declare_table schema ~name:"person"
Schema.[field "id" ~ty:Type.int; field "name" ~ty:Type.text];;

let (pet, Expr.[pet_id; pet_name; owner_id]) = StaticSchema.declare_table schema ~name:"pet"
Schema.[field "id" ~ty:Type.int; field "name" ~ty:Type.text; field "owner" ~ty:Type.int];;

Then I'd assume I could write a join query as follow:

Query.select ~from:person Expr.[id; name; pet_name]
|> Query.join ~on:Expr.(id = owner_id) (Query.select ~from:pet Expr.[owner_id; pet_name])
|> Format.asprintf "%a" Query.pp;;

This produces:

SELECT person.id, person.name, pet.name
FROM person INNER JOIN (SELECT pet.owner, pet.name
FROM pet) AS join_tmp_0 ON person.id = pet.owner

So the inner select on the pet table has been aliased to join_tmp_0 but the outer select and the on clause still use the pet prefix.

I assume I misundertood something in the join API, but I could find any relevant example.