valiant-mtl

MTL-style adapter for valiant.

All operations work in any monad with HasPool m (a MonadReader-like class that exposes a Pool) and MonadIO m. Use this when your application lives in an mtl stack with a richer environment than just Pool.

Quick start

import Control.Monad.Reader
import Valiant (newPool, defaultPoolConfig, poolConnString)
import Valiant.Mtl

data AppEnv = AppEnv
  { appPool   :: Pool
  , appLogger :: Logger
  }

instance HasPool (ReaderT AppEnv IO) where
  getPool = asks appPool

myApp :: (HasPool m, MonadIO m) => m [User]
myApp = do
  users <- fetchAllMtl listUsers ()
  count <- fetchScalarMtl countUsers ()
  pure users

main :: IO ()
main = do
  pool   <- newPool defaultPoolConfig { poolConnString = "postgres://..." }
  logger <- newLogger
  runReaderT myApp (AppEnv pool logger)

What you get

• class HasPool m where getPool :: m Pool
• Query operations: fetchOneMtl, fetchAllMtl, fetchScalarMtl, fetchOneOrThrowMtl, fetchExistsMtl, forEachMtl
• Command operations: executeMtl, executeReturningMtl, executeBatchMtl
• Transactions: withTransactionMtl, withTransactionLevelMtl
• Pool helpers: poolStatsMtl, withConnectionMtl

There is also a Valiant.Monad module re-exported from this package that provides the same operations specialised to ReaderT Pool IO.

See the valiant tutorial for Statement definitions and the valiant prepare workflow.