Safe Haskell	None
Language	Haskell2010

Preql.Effect.Internal

Contents

Transactions

Description

We use IO in the representation of Transaction, but we don't want to allow arbitrary IO, only SQL queries. So keep it private.

The SQL class refers to Transaction, and the Transaction instance refers to the class, so it all needs to be here.

Synopsis

class Monad m => SQL (m :: * -> *) where
- query :: (ToSql p, FromSql r) => (Query, p) -> m (Vector r)
- query_ :: ToSql p => (Query, p) -> m ()
- runTransaction :: Transaction a -> m a
newtype Transaction a = Transaction (ExceptT QueryError (ReaderT Connection IO) a)
runTransactionIO :: Transaction a -> Connection -> IO (Either QueryError a)

Documentation

class Monad m => SQL (m :: * -> *) where Source #

An Effect class for running SQL queries. You can think of this as a context specifying a particular Postgres connection (or connection pool). A minimal instance defines runTransaction. A typical instance will use runTransactionIO or functions in Query and log & rethrow errors.

Minimal complete definition

runTransaction

Methods

query :: (ToSql p, FromSql r) => (Query, p) -> m (Vector r) Source #

Run a parameterized query that returns data. The tuple argument is typically provided by the sql Quasiquoter.

query_ :: ToSql p => (Query, p) -> m () Source #

Run a parameterized query that does not return data.

runTransaction :: Transaction a -> m a Source #

Run multiple queries in a transaction.

Instances

SQL Transaction Source #	The same `query` methods can be used within a `Transaction`. Nested `Transactions` are implemented using savepoints.
Instance details Defined in Preql.Effect.Internal Methods query :: (ToSql p, FromSql r) => (Query, p) -> Transaction (Vector r) Source # query_ :: ToSql p => (Query, p) -> Transaction () Source # runTransaction :: Transaction a -> Transaction a Source #
(MonadTrans t, Monad (t m), SQL m) => SQL (t m) Source #	Lift through any monad transformer without a more specific instance.
Instance details Defined in Preql.Effect.Internal Methods query :: (ToSql p, FromSql r) => (Query, p) -> t m (Vector r) Source # query_ :: ToSql p => (Query, p) -> t m () Source # runTransaction :: Transaction a -> t m a Source #
SQL (ReaderT Connection IO) Source #	Most larger applications will define an instance; this one is suitable to test out the library.
Instance details Defined in Preql.Effect.Internal Methods query :: (ToSql p, FromSql r) => (Query, p) -> ReaderT Connection IO (Vector r) Source # query_ :: ToSql p => (Query, p) -> ReaderT Connection IO () Source # runTransaction :: Transaction a -> ReaderT Connection IO a Source #

Transactions

newtype Transaction a Source #

A Transaction can only contain SQL queries (and pure functions).

Constructors

Transaction (ExceptT QueryError (ReaderT Connection IO) a)

Instances

Monad Transaction Source #
Instance details Defined in Preql.Effect.Internal Methods (>>=) :: Transaction a -> (a -> Transaction b) -> Transaction b # (>>) :: Transaction a -> Transaction b -> Transaction b # return :: a -> Transaction a # fail :: String -> Transaction a #
Functor Transaction Source #
Instance details Defined in Preql.Effect.Internal Methods fmap :: (a -> b) -> Transaction a -> Transaction b # (<$) :: a -> Transaction b -> Transaction a #
Applicative Transaction Source #
Instance details Defined in Preql.Effect.Internal Methods pure :: a -> Transaction a # (<>) :: Transaction (a -> b) -> Transaction a -> Transaction b # liftA2 :: (a -> b -> c) -> Transaction a -> Transaction b -> Transaction c # (>) :: Transaction a -> Transaction b -> Transaction b # (<*) :: Transaction a -> Transaction b -> Transaction a #
SQL Transaction Source #	The same `query` methods can be used within a `Transaction`. Nested `Transactions` are implemented using savepoints.
Instance details Defined in Preql.Effect.Internal Methods query :: (ToSql p, FromSql r) => (Query, p) -> Transaction (Vector r) Source # query_ :: ToSql p => (Query, p) -> Transaction () Source # runTransaction :: Transaction a -> Transaction a Source #

runTransactionIO :: Transaction a -> Connection -> IO (Either QueryError a) Source #

Run the provided Transaction. If it fails with a QueryError, roll back.