ppx_rapper

Syntax extension for Caqti/PostgreSQL queries
README

An extension that allows named parameters in SQL with types inferred, and syntax checking of SQL as a preprocessing
step. Like ppx_mysql but using Caqti/PostgreSQL/LWT. The name comes from being
Dapper but with Records.

Usage

Example

let my_query =
  [%rapper
    get_opt
      {sql|
      SELECT @int{id}, @string{username}, @bool{following}, @string?{bio}
      FROM users
      WHERE username <> %string{wrong_user} AND id > %int{min_id}
      |sql}]

turns into

let my_query =
  let query =
    (let open Caqti_request in
    find_opt)
      (let open Caqti_type in
      tup2 string int)
      (let open Caqti_type in
      tup2 int (tup2 string (tup2 bool (option string))))
      "\n\
      \      SELECT id, username, following, bio\n\
      \      FROM users\n\
      \      WHERE username <> ? AND id > ?\n\
      \      "
  in
  let wrapped (module Db : Caqti_lwt.CONNECTION) ~wrong_user ~min_id =
    let f result =
      let g (id, (username, (following, bio))) =
        (id, username, following, bio)
      in
      Result.map ~f:(Option.map ~f:g) result
    in
    Lwt.map f (Db.find_opt query (wrong_user, min_id))
  in
  wrapped

Query functions

Query functions are

  • execute for queries that return 0 rows, represented as ()

  • get_one for queries that return 1 rows, represented as a tuple/record

  • get_opt for queries that return 0 or 1 rows, represented as a tuple/record option

  • get_many for queries that many return any number of rows, represented as a list of tuples/records

These correspond to exec, find, find_opt and collect in Caqti_request.

Parameters

Syntax for input/output parameters is the same as ppx_mysql: %type{name} for
inputs and @type{name} for outputs. Currently supported base types are int, string and bool, plus options of
those specified with type?. Lists and custom types from ppx_mysql are not implemented yet.

Options

If record_in or record_out are given as options like so:

let my_query =
  [%rapper
    get_opt
      {sql|
      SELECT @int{id}, @string{username}, @bool{following}, @string?{bio}
      FROM users
      WHERE username <> %string{wrong_user} AND id > %int{min_id}
      |sql}
      record_in record_out]

then the input and/or output of the query will be records. For the example above, they would have type {id: int; wrong_user: string} and {id: int; username: string; following: bool; bio: string option} respectively. The default non-record methods are labelled arguments and tuples respectively.

By default, queries are syntax checked using pg_query-ocaml and the
extension will error if syntax checking fails. If this gives a false positive error for a query it can be stopped using the syntax_off option.

Requirements

The runtime requirements of Rapper are core, lwt, caqti, caqti-lwt and caqti-driver-postgresql.

Install
Published
22 Dec 2019
Sources
0.9.2.tar.gz
md5=89a2f61dc724b40f5f74ffac2249c04d
sha512=77db01bc1e5e6b55134c14b443084b30c2fb830b12706fcfa945921e2cc124feeb4baba8d9af68af709bc5d457dda78099b9ccca387783f5f7703cce95bc1aa5
Dependencies
Reverse Dependencies