Preql.Effect

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

Documentation

data Query

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

Instances

Show Query

Defined in Preql.Wire.Internal

Methods

showsPrec :: Int -> Query -> ShowS

show :: Query -> String

showList :: [Query] -> ShowS

IsString Query

Defined in Preql.Wire.Internal

Methods

fromString :: String -> Query

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

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)

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

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

Run a parameterized query that does not return data.

runTransaction :: Transaction a -> m a

Run multiple queries in a transaction.

Instances

SQL Transaction

The same query methods can be used within a Transaction. Nested Transactions are implemented using savepoints.

Defined in Preql.Effect.Internal

Methods

query :: (ToSql p, FromSql r) => (Query, p) -> Transaction (Vector r)

query_ :: ToSql p => (Query, p) -> Transaction ()

runTransaction :: Transaction a -> Transaction a

(MonadTrans t, Monad (t m), SQL m) => SQL (t m)

Lift through any monad transformer without a more specific instance.

Defined in Preql.Effect.Internal

Methods

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

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

runTransaction :: Transaction a -> t m a

SQL (ReaderT Connection IO)

Most larger applications will define an instance; this one is suitable to test out the library.

Defined in Preql.Effect.Internal

Methods

query :: (ToSql p, FromSql r) => (Query, p) -> ReaderT Connection IO (Vector r)

query_ :: ToSql p => (Query, p) -> ReaderT Connection IO ()

runTransaction :: Transaction a -> ReaderT Connection IO a

data Transaction a

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

Instances

Monad Transaction

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

Defined in Preql.Effect.Internal

Methods

fmap :: (a -> b) -> Transaction a -> Transaction b

(<$) :: a -> Transaction b -> Transaction a

Applicative Transaction

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

The same query methods can be used within a Transaction. Nested Transactions are implemented using savepoints.

Defined in Preql.Effect.Internal

Methods

query :: (ToSql p, FromSql r) => (Query, p) -> Transaction (Vector r)

query_ :: ToSql p => (Query, p) -> Transaction ()

runTransaction :: Transaction a -> Transaction a

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

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