fake-package.cabal

cabal-version: 2.2
name:          fake-package
version:       0

executable script
    main-is:            Main.hs
    other-modules:
        Templates
        LocalQ

    default-language:   Haskell2010
    default-extensions: TemplateHaskell, TypeSynonymInstances, MultiParamTypeClasses, ScopedTypeVariables, FlexibleInstances, OverloadedStrings
    ghc-options:        -ddump-splices -ddump-to-file
    build-depends:
        base,
        opaleye,
        template-haskell,
        pretty-show,
        postgresql-simple,
        mtl, transformers
        , product-profunctors

Main.hs

module Main where

import Data.Foldable
import Database.PostgreSQL.Simple
import Database.PostgreSQL.Simple.FromField
import qualified Opaleye
import Templates

makeOpaleyeInterface
  TableIdentifier {maybeNameOfSchema = Just "information_schema", nameOfTable = "columns"}
  [ ColumnDescription {nameOfColumn = "table_schema", typeOfColumn = ''Opaleye.PGText, haskellType = ''String}
  , ColumnDescription {nameOfColumn = "table_name", typeOfColumn = ''Opaleye.PGText, haskellType = ''String}
  , ColumnDescription {nameOfColumn = "column_name", typeOfColumn = ''Opaleye.PGText, haskellType = ''String}
  , ColumnDescription {nameOfColumn = "data_type", typeOfColumn = ''Opaleye.PGText, haskellType = ''String}
  ]

main :: IO ( )
main = do
  connection <- connectPostgreSQL "host=localhost dbname=example"
  columns :: [Haskell__'information_schema__columns'] <-
    runSelect__'information_schema__columns' connection
  traverse_ print columns

Example for Opaleye Templates.