Safe Haskell	None
Language	Haskell2010

Hasql.Postgres

Description

This module contains everything required to use "hasql" with Postgres. For information on how it should be used consult the "hasql" docs.

Please note that there is a few limitations inflicted by Postgres, encoding which in the type system would seriously burden the API, so it was decided to make it the user's responsibility to make sure that certain conditions are satisfied during the runtime. Particularly this concerns the Mapping instances of Maybe, [] and Vector. For details consult the docs on those instances.

Synopsis

Documentation

data Postgres Source

Settings of a Postgres backend.

Constructors

Postgres
Fields host :: ByteString port :: Word16 user :: Text password :: Text database :: Text

Instances

Backend Postgres
Mapping Postgres Bool	Maps to `bool`.
Mapping Postgres Char	Maps to `char`. Note that it supports UTF-8 values.
Mapping Postgres Double	Maps to `float8`.
Mapping Postgres Float	Maps to `float4`.
Mapping Postgres Int	Maps to `int8`.
Mapping Postgres Int8	Maps to `int2`.
Mapping Postgres Int16	Maps to `int2`.
Mapping Postgres Int32	Maps to `int4`.
Mapping Postgres Int64	Maps to `int8`.
Mapping Postgres Word	Maps to `int8`.
Mapping Postgres Word8	Maps to `int2`.
Mapping Postgres Word16	Maps to `int2`.
Mapping Postgres Word32	Maps to `int4`.
Mapping Postgres Word64	Maps to `int8`.
Mapping Postgres ByteString	Maps to `bytea`.
Mapping Postgres Text	Maps to `text`.
Mapping Postgres UUID	Maps to `uuid`.
Mapping Postgres DiffTime	Maps to `interval`.
Mapping Postgres Day	Maps to `date`.
Mapping Postgres UTCTime	Maps to `timestamp`.
Mapping Postgres TimeOfDay	Maps to `time`.
Mapping Postgres LocalTime	Maps to `timestamptz`. NOTICE Postgres does not store the timezone information of `timestamptz`. Instead it stores a UTC value and silently interconverts the incoming and outgoing values into a local time of the client application according to client application's timezone. This is a notoriously questionable design decision by the Postgres authors. This is why it is instead recommended to use `timestamp` and `UTCTime`, while manually handling the timezone conversions on the application side.
Mapping Postgres Scientific	Maps to `numeric`.
(Mapping a, ArrayMapping a) => Mapping Postgres [a]	Maps to Postgres arrays. LIMITATION 1 In multidimensional lists all rows of a dimension must have the same length. E.g., the following is a corrupt value: [[1,2], [3]] The following is a valid one: [[1,2], [3,4], [5,6]] LIMITATION 2 `Maybe` cannot be used to wrap an intermediate level in a multidimensional array. E.g., the following is a corrupt type: [Maybe [a]] However, both the first level list and the value are allowed to be wrapped in `Maybe`. So the following is a valid type: Maybe [[[Maybe a]]] NOTICE Also, please note that since `String` is just an alias to `[Char]`, it will be mapped to an array of characters. So if you want to map to a textual type use `Text` instead.
Mapping a => Mapping Postgres (Maybe a)	Maps to the same type as the underlying value, encoding `Nothing` as NULL. LIMITATION Multilevel `Maybe`s are not supported. E.g., a value `Just Nothing` of type `(Maybe (Maybe a))` will be encoded the same way as `Nothing`.
(Mapping a, ArrayMapping a) => Mapping Postgres (Vector a)	Maps to Postgres' arrays. Same rules as for the list instance apply. Consult its docs for details.
Mapping Postgres (TimeOfDay, TimeZone)	Maps to `timetz`. Unlike with `timestamptz`, Postgres does store the timezone information for `timetz`. However the "time" library does not contain any composite type, that fits the task, so we use a pair of `TimeOfDay` and `TimeZone` to represent a value on the Haskell's side.
data Connection Postgres = Connection { connection :: !Connection preparer :: !StatementPreparer transactionState :: !(IORef (Maybe Word)) }
data Result Postgres = Result { unpackResult :: Maybe ByteString }
data StatementArgument Postgres = StatementArgument { unpackStatementArgument :: (Oid, Maybe (ByteString, Format)) }