Add Connection type

lib/Database/PostgreSQL/Opium/Connection.hs

@@ -0,0 +1,39 @@
+{-# LANGUAGE LambdaCase #-}
+
+module Database.PostgreSQL.Opium.Connection
+  ( Connection
+  , unsafeWithRawConnection
+  , withRawConnection
+  , connect
+  , close
+  ) where
+
+import Data.ByteString (ByteString)
+import GHC.Stack (HasCallStack)
+
+import qualified Database.PostgreSQL.LibPQ as LibPQ
+
+newtype Connection = Connection LibPQ.Connection
+
+withRawConnection
+  :: (Maybe LibPQ.Connection -> m a)
+  -> Connection
+  -> m a
+withRawConnection f (Connection rawConn) = f (Just rawConn)
+
+unsafeWithRawConnection
+  :: HasCallStack
+  => (LibPQ.Connection -> m a)
+  -> Connection
+  -> m a
+unsafeWithRawConnection f = withRawConnection $ \case
+  Nothing -> error "raw connection is missing! perhaps the connection was already closed."
+  Just rawConn -> f rawConn
+
+connect :: ByteString -> IO Connection
+connect connectionString = do
+  rawConn <- LibPQ.connectdb connectionString
+  pure $ Connection rawConn
+
+close :: Connection -> IO ()
+close (Connection rawConn) = LibPQ.finish rawConn

lib/Database/PostgreSQL/Opium/Error.hs

@@ -19,6 +19,7 @@ data Error
   | ErrorInvalidField ErrorPosition Oid ByteString String
   | ErrorNotExactlyOneRow
   | ErrorMoreThanOneRow
+  | ErrorConnectionClosed
   deriving (Eq, Show)
 
 instance Exception Error where