caqti-async

Async support for Caqti
README

Synopsis

Caqti provides a monadic cooperative-threaded OCaml connector API for
relational databases.

The purpose of Caqti is further to help make applications independent of a
particular database system. This is achieved by defining a common
signature, which is implemented by the database drivers. Connection
parameters are specified as an URI, which is typically provided at run-time.
Caqti then loads a driver which can handle the URI, and provides a
first-class module which implements the driver API and additional
convenience functionality.

Caqti does not make assumptions about the structure of the query language,
and only provides the type information needed at the edges of communication
between the OCaml code and the database; i.e. for encoding parameters and
decoding returned tuples. It is hoped that this agnostic choice makes it a
suitable target for higher level interfaces and code generators.

Drivers

The following drivers are available.

  • MariaDB (mariadb://)

    • Implemented in terms of
      ocaml-mariadb
      using asynchronous calls.

    • Supports transactions.

    • Pools connections and caches statements.

  • PostgreSQL (postgresql://)

    • Implemented in terms of
      postgresql-ocaml
      using asynchronous calls.

    • Supports transactions.

    • Pools connections and caches statements.

  • SQLite3 (sqlite3://)

    • Implemented in terms of
      sqlite3-ocaml
      using preemtive threading for non-blocking operation.

    • Supports transactions.

    • Does not pool connections or cache statements.

If you link against caqti-dynload, then drivers are loaded dynamically
based on the URI. If dynamic loading is unavailable on your platform, you
may instead link against the caqti-driver-* libraries which you expect to
use.

Documentation

For a gentle introduction I recommend reading Interfacing OCaml and
PostgreSQL with Caqti
by Bobby Priambodo. There is also a
documented example in this repository.

A resent rendering of the full API reference is available online.
You can also generate the API reference matching your installed version
using odig. Finally, topkg doc builds the reference from a Git
checkout using topkg-care.

As the main entry point, you would normally use either of

Caqti_lwt : Caqti_connection_sig.S with type 'a io = 'a Lwt.t
Caqti_async : Caqti_connection_sig.S with type 'a io = 'a Deferred.t

which is provided by caqti-lwt or caqti-async, respectively. These
provide a connect functions which receives an URI, loads the appropriate
driver, and returns a connection as a first-class module containing query
functionality for the database.

The most important modules to know about are:

  • Caqti_type and Caqti_request for constructing prepared or one-shot
    queries.

  • Caqti_lwt and Caqti_async for connecting to the database and
    obtaining a first class module implementing Caqti_connection_sig.S.

  • Caqti_connection_sig.S and Caqti_response_sig.S for executing
    queries.

Running under utop

Dynamic linking does not work under utop. The workaround is to link against
the needed database driver. E.g.

> #require "caqti-lwt";;
> #require "caqti-driver-postgresql";;
> open Lwt.Infix;;

(* Create a DB handle. *)
> module Db = (val Caqti_lwt.connect (Uri.of_string "postgresql://") >>= Caqti_lwt.or_fail |> Lwt_main.run);;
module Db : Caqti_lwt.CONNECTION

(* Create a request which merely adds two parameters. *)
> let plus = Caqti_request.find Caqti_type.(tup2 int int) Caqti_type.int "SELECT ?::integer + ?::integer";;
val plus : (int * int, int, [< `Many | `One | `Zero > `One ]) Caqti_request.t = <abstr>

(* Run it. *)
> Db.find plus (7, 13);;
- : (int, [> Caqti_error.call_or_retrieve ]) result = Ok 20
Install
Published
20 Sep 2018
Sources
caqti-1.0.0.tbz
md5=6fb535971d307094a9f0bfb05ddc711c
sha256=016e4649710b8ba530642aa706fa62ae65224f18d6791df63554451a430eb3dd
Dependencies
core
< "v0.13"
caqti-driver-sqlite3
with-test & >= "1.0.0" & < "2.0.0~"
caqti-dynload
with-test & >= "1.0.0" & < "2.0.0~"
caqti
>= "1.0.0" & < "1.2.0~"
async
>= "v0.11.0" & < "v0.13"
Reverse Dependencies