Safe Haskell	None
Language	Haskell2010

Hasql.Session

Synopsis

data Session a
pipeline :: Pipeline result -> Session result
script :: Text -> Session ()
statement :: params -> Statement params result -> Session result
onLibpqConnection :: (Connection -> IO (Either SessionError a, Connection)) -> Session a

Documentation

data Session a Source #

A sequence of operations to be executed in the context of a single database connection with exclusive access to it.

Construct sessions using helpers in this module such as statement, pipeline and script, or use onLibpqConnection for a low-level escape hatch.

To actually execute a Session use use, which manages concurrent access to the shared connection state and returns either a SessionError or the result:

result <- Hasql.Connection.use connection mySession

Note: while most session errors are returned as values, user code executed inside a session may still throw exceptions; in that case the driver will reset the connection to a clean state.

Instances

Instances details

MonadIO Session Source #
Instance details Defined in Hasql.Engine.Contexts.Session Methods liftIO :: IO a -> Session a #
Applicative Session Source #
Instance details Defined in Hasql.Engine.Contexts.Session Methods pure :: a -> Session a # (<>) :: Session (a -> b) -> Session a -> Session b # liftA2 :: (a -> b -> c) -> Session a -> Session b -> Session c # (>) :: Session a -> Session b -> Session b # (<*) :: Session a -> Session b -> Session a #
Functor Session Source #
Instance details Defined in Hasql.Engine.Contexts.Session Methods fmap :: (a -> b) -> Session a -> Session b # (<$) :: a -> Session b -> Session a #
Monad Session Source #
Instance details Defined in Hasql.Engine.Contexts.Session Methods (>>=) :: Session a -> (a -> Session b) -> Session b # (>>) :: Session a -> Session b -> Session b # return :: a -> Session a #
MonadError SessionError Session Source #
Instance details Defined in Hasql.Engine.Contexts.Session Methods throwError :: SessionError -> Session a # catchError :: Session a -> (SessionError -> Session a) -> Session a #

pipeline :: Pipeline result -> Session result Source #

Execute a pipeline.

script :: Text -> Session () Source #

Possibly a multi-statement query, which however cannot be parameterized or prepared, nor can any results of it be collected.

statement :: params -> Statement params result -> Session result Source #

Execute a statement by providing parameters to it.

onLibpqConnection :: (Connection -> IO (Either SessionError a, Connection)) -> Session a Source #

Execute an operation on the raw libpq connection possibly producing an error and updating the connection. This is a low-level escape hatch for custom integrations.

You can supply a new connection in the result to replace it in the running Hasql connection. The responsibility to close the old libpq connection is on you. Otherwise, just return the same connection you've received.

Producing a Left value will cause the session to fail with the given error. Regardless of success or failure, the connection will be replaced with the one you return.

Throwing exceptions is okay. It will lead to the connection getting reset.