Module DataSource

Use this module to query the database, implement and run migrations, clean repositories, turn HTTP queries into SQL queries or for sane entity identifier handling.

Installation

The database service uses https://github.com/paurkedal/ocaml-caqti under the hood. Caqti can dynamically load the correct driver based on the DATABASE_URL (postgresql://).

Caqti supports following databases (caqti drivers):

• PostgreSQL (caqti-driver-postgresql)
• MariaDB (caqti-driver-mariadb)
• SQLite (caqti-driver-sqlite)

module Log = Sihl.Log.Service.Make ()
module Config = Sihl.Config.Service.Make (Log)
module Db = Sihl.Data.Db.Service.Make (Config) (Log)

Install one of the drivers listed above.

opam install caqti-driver-postgresql

Add the driver to your done file:

caqti-driver-postgresql

Usage

Register the database middleware, so other services can query the database with the context that contains the database pool.

module DbMiddleware = Sihl.Web.Middleware.Db.Make (Service.Db)
let middlewares = [
  DbMiddleware.m();
]

The database service should be used mostly in repositories and not in services themselves.

pizza_order_repo.ml:

module MakePostgreSql
    (DbService: Sihl.Data.Db.Service.Sig.SERVICE) : Pizza_order_sig.REPO =
struct

  let find_request =
    Caqti_request.find_opt Caqti_type.string Model.t
      {sql|
        SELECT
          uuid,
          customer,
          pizza,
          amount,
          status,
          confirmed,
          created_at,
          updated_at
        FROM pizza_orders
        WHERE pizza_orders.uuid = ?::uuid
        |sql}

  let find ctx ~id =
    DbService.query ctx (fun connection ->
        let module Connection = (val connection : Caqti_lwt.CONNECTION) in
        Connection.find_opt get_request id
        |> Lwt_result.map_err Caqti_error.show)

end

pizza_order_service.ml:

module Make
    (Repo: Pizza_order_sig.REPO) : Pizza_order_sig.SERVICE = struct

    let find ctx ~id = Repo.find ctx ~id
end

Then you can use the service:

module PizzaOrderRepo = Pizza_order_repo.MakePostgreSql (Service.Db)
module PizzaOrderService = Pizza_order_service.Make (PizzaOrderRepo)
let get_pizza_order =
  Sihl.Web.Route.get "/pizza-orders/:id" (fun ctx ->
      Sihl.Web.Res.(html |> set_body "Hello!") |> Lwt.return)
let get_pizza_order =
  Sihl.Web.Route.get "/pizza-orders/:id" (fun ctx ->
      let id = Sihl.Web.Req.param ctx "id" in
      let pizza = PizzaOrderService.find ctx ~id in
      ...
      )