effectful support for high-level PostgreSQL operations via Opaleye.

See the README for an overview, or the documentation in Effectful.Opaleye.

effectful-opaleye

This package provides an effectful effect for Opaleye operations.

It combines the very safe, high-level syntax of Opaleye, with the WithConnection abstraction of effectful-postgresql.

Effectful functions

In the Opaleye effect we can perform the 4 main operations permitted by Opaleye: query, insert, delete, and update.

{-# LANGUAGE Arrows #-}
import Control.Arrow
import Effectful.Opaleye as EO
import qualified Opaleye as O

insertAndList :: (EO.Opaleye :> es) => Eff es [User]
insertAndList = do
  EO.runInsert $ O.Insert userTable [User {firstName = "Nuala"}] O.rCount Nothing

  EO.runDelete $ O.Delete userTable isAdmin O.rCount

  EO.runUpdate $ O.Update userTable (\user -> user {updatedAt = O.now}) isAdmin O.rCount

  EO.runSelect $ proc () -> do
    user <- O.selectTable userTable -< ()
    O.restrict -< firstName user `O.in_` (O.toFields <$> ["Anna", "Boris", "Carla"])
    returnA -< user

Interpreters

To run the Opaleye effect we can use the WithConnection effect from effectful-postgresql:

import Effectful.PostgreSQL as EP
import Effectful.Opaleye as EO

doOpaleyeStuff :: (WithConnection :> es) => Eff es [User]
doOpaleyeStuff = EO.runOpaleyeWithConnection insertAndList

The WithConnection effect can then be dispatched using one of its interpreters. Or, to skip that entirely, we can just use runOpaleyeConnection:

doOpaleyeStuff :: PSQL.Connection -> Eff es [User]
doOpaleyeStuff conn = EO.runOpaleyeConnection conn insertAndList