Safe Haskell	None
Language	Haskell2010

Preql.Effect

Description

SQL Effect class, basically capturing some way of accessing a database.

Synopsis

data Query
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
data Transaction a
runTransactionIO :: Transaction a -> Connection -> IO (Either QueryError a)

Documentation

data Query Source #

The IsString instance does no validation; the limited instances discourage directly manipulating strings, with the high risk of SQL injection.

Instances

Show Query Source #
Instance details Defined in Preql.Wire.Internal Methods showsPrec :: Int -> Query -> ShowS # show :: Query -> String # showList :: [Query] -> ShowS #
IsString Query Source #
Instance details Defined in Preql.Wire.Internal Methods fromString :: String -> Query #

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 #

data Transaction a Source #

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

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.