Hasql.Session

Documentation

data Session a

A batch of actions to be executed in the context of a database connection.

Instances

Monad Session

Methods

(>>=) :: Session a -> (a -> Session b) -> Session b

(>>) :: Session a -> Session b -> Session b

return :: a -> Session a

fail :: String -> Session a

Functor Session

Methods

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

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

Applicative Session

Methods

pure :: a -> Session a

(<*>) :: Session (a -> b) -> Session a -> Session b

(*>) :: Session a -> Session b -> Session b

(<*) :: Session a -> Session b -> Session a

MonadIO Session

Methods

liftIO :: IO a -> Session a

MonadError Error Session

Methods

throwError :: Error -> Session a

catchError :: Session a -> (Error -> Session a) -> Session a

sql :: ByteString -> Session ()

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

query :: a -> Query a b -> Session b

Parameters and a specification of the parametric query to apply them to.

Execution

data Error

An error of some command in the session.

Constructors

ClientError !(Maybe ByteString)

An error on the client-side, with a message generated by the "libpq" library. Usually indicates problems with connection.

ResultError !ResultError

Some error with a command result.

Instances

Eq Error

Methods

(==) :: Error -> Error -> Bool

(/=) :: Error -> Error -> Bool

Show Error

Methods

showsPrec :: Int -> Error -> ShowS

show :: Error -> String

showList :: [Error] -> ShowS

MonadError Error Session

Methods

throwError :: Error -> Session a

catchError :: Session a -> (Error -> Session a) -> Session a

data ResultError

An error with a command result.

Constructors

ServerError !ByteString !ByteString !(Maybe ByteString) !(Maybe ByteString)

An error reported by the DB. Consists of the following: Code, message, details, hint.

• Code. The SQLSTATE code for the error. It's recommended to use the "postgresql-error-codes" package to work with those.
• Message. The primary human-readable error message (typically one line). Always present.
• Details. An optional secondary error message carrying more detail about the problem. Might run to multiple lines.
• Hint. An optional suggestion on what to do about the problem. This is intended to differ from detail in that it offers advice (potentially inappropriate) rather than hard facts. Might run to multiple lines.

UnexpectedResult !Text

The database returned an unexpected result. Indicates an improper statement or a schema mismatch.

RowError !Int !RowError

An error of the row reader, preceded by the index of the row.

UnexpectedAmountOfRows !Int

An unexpected amount of rows.

Instances

Eq ResultError

Methods

(==) :: ResultError -> ResultError -> Bool

(/=) :: ResultError -> ResultError -> Bool

Show ResultError

Methods

showsPrec :: Int -> ResultError -> ShowS

show :: ResultError -> String

showList :: [ResultError] -> ShowS

data RowError

An error during the decoding of a specific row.

Constructors

EndOfInput

Appears on the attempt to parse more columns than there are in the result.

UnexpectedNull

Appears on the attempt to parse a NULL as some value.

ValueError !Text

Appears when a wrong value parser is used. Comes with the error details.

Instances

Eq RowError

Methods

(==) :: RowError -> RowError -> Bool

(/=) :: RowError -> RowError -> Bool

Show RowError

Methods

showsPrec :: Int -> RowError -> ShowS

show :: RowError -> String

showList :: [RowError] -> ShowS

run :: Session a -> Connection -> IO (Either Error a)

Executes a bunch of commands on the provided connection.