package caqti-type-calendar
Install
Dune Dependency
Authors
Maintainers
Sources
sha256=37482ccb5866d4d195f206a88cf764b7f3fd483e159c1b643e767e5cf51335ff
md5=f749fd41e5c20d20a315f257f6ec7128
README.md.html
README.md
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
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.
To get a quick idea of how to use Caqti, look at the documented example. A resent rendering of the full API reference is avaliable online. You can generate the API reference matching your installed version using odig. Finally, topkg doc
builds the reference for a Git checkout.
The most important modules to know about are:
Caqti_type
andCaqti_request
for constructing prepared or one-shot queries.Caqti_lwt
andCaqti_async
for connecting to the database and obtaining a first class module implementingCaqti_connection_sig.S
.Caqti_connection_sig.S
andCaqti_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