hasql- A very efficient PostgreSQL driver and a flexible mapping API

Safe HaskellNone




A DSL for declaration of query parameter encoders.



data Params a Source

Encoder of some representation of the parameters product.

Has instances of Contravariant, Divisible and Monoid, which you can use to compose multiple parameters together. E.g.,

someParamsEncoder :: Params (Int64, Maybe Text)
someParamsEncoder =
  contramap fst (value int8) <>
  contramap snd (nullableValue text)

As a general solution for tuples of any arity, instead of fst and snd, consider the functions of the contrazip family from the "contravariant-extras" package. E.g., here's how you can achieve the same as the above:

someParamsEncoder :: Params (Int64, Maybe Text)
someParamsEncoder =
  contrazip2 (value int8) (nullableValue text)

Here's how you can implement encoders for custom composite types:

data Person =
  Person { name :: Text, gender :: Gender, age :: Int }

data Gender =
  Male | Female

personParams :: Params Person
personParams =
  contramap name (value text) <>
  contramap gender (value genderValue) <>
  contramap (fromIntegral . age) (value int8)

genderValue :: Value Gender
genderValue =
  contramap genderText text
    genderText gender =
      case gender of
        Male -> "male"
        Female -> "female"


Divisible Params Source 
Contravariant Params Source 
Monoid (Params a) Source 
Default (Params ()) Source

Maps to unit.

(Default (Value a1), Default (Value a2)) => Default (Params (a1, a2)) Source 
(Default (Value a1), Default (Value a2), Default (Value a3)) => Default (Params (a1, a2, a3)) Source 
(Default (Value a1), Default (Value a2), Default (Value a3), Default (Value a4)) => Default (Params (a1, a2, a3, a4)) Source 
(Default (Value a1), Default (Value a2), Default (Value a3), Default (Value a4), Default (Value a5)) => Default (Params (a1, a2, a3, a4, a5)) Source 
Default (Value a) => Default (Params (Identity a)) Source 

unit :: Params () Source

Encode no parameters.

value :: Value a -> Params a Source

Lift an individual value encoder to a parameters encoder.

nullableValue :: Value a -> Params (Maybe a) Source

Lift an individual nullable value encoder to a parameters encoder.


bool :: Value Bool Source

Encoder of BOOL values.

int2 :: Value Int16 Source

Encoder of INT2 values.

int4 :: Value Int32 Source

Encoder of INT4 values.

int8 :: Value Int64 Source

Encoder of INT8 values.

float4 :: Value Float Source

Encoder of FLOAT4 values.

float8 :: Value Double Source

Encoder of FLOAT8 values.

numeric :: Value Scientific Source

Encoder of NUMERIC values.

char :: Value Char Source

Encoder of CHAR values. Note that it supports UTF-8 values and identifies itself under the TEXT OID because of that.

text :: Value Text Source

Encoder of TEXT values.

bytea :: Value ByteString Source

Encoder of BYTEA values.

date :: Value Day Source

Encoder of DATE values.

timestamp :: Value LocalTime Source

Encoder of TIMESTAMP values.

timestamptz :: Value UTCTime Source

Encoder of TIMESTAMPTZ values.

time :: Value TimeOfDay Source

Encoder of TIME values.

timetz :: Value (TimeOfDay, TimeZone) Source

Encoder of TIMETZ values.

interval :: Value DiffTime Source

Encoder of INTERVAL values.

uuid :: Value UUID Source

Encoder of UUID values.

json :: Value Value Source

Encoder of JSON values.

array :: Array a -> Value a Source

Unlifts the Array encoder to the plain Value encoder.

enum :: (a -> Text) -> Value a Source

Given a function, which maps the value into the textual enum label from the DB side, produces a encoder of that value.


data Array a Source

A generic array encoder.

Here's an example of its usage:

x :: Value [[Int64]]
x =
  array (arrayDimension foldl' (arrayDimension foldl' (arrayValue int8)))

arrayValue :: Value a -> Array a Source

Lifts the Value encoder into the Array encoder of a non-nullable value.

arrayNullableValue :: Value a -> Array (Maybe a) Source

Lifts the Value encoder into the Array encoder of a nullable value.

arrayDimension :: (forall a. (a -> b -> a) -> a -> c -> a) -> Array b -> Array c Source

An encoder of an array dimension, which thus provides support for multidimensional arrays.