Hasql.Encoders

A DSL for declaration of query parameter encoders.

Params

data Params a

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 (nullableParam 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) (nullableParam 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
  where
    genderText gender =
      case gender of
        Male -> "male"
        Female -> "female"

Instances

Divisible Params

Methods

divide :: (a -> (b, c)) -> Params b -> Params c -> Params a

conquer :: Params a

Decidable Params

Methods

lose :: (a -> Void) -> Params a

choose :: (a -> Either b c) -> Params b -> Params c -> Params a

Contravariant Params

Methods

contramap :: (a -> b) -> Params b -> Params a

(>$) :: b -> Params b -> Params a

Semigroup (Params a)

Methods

(<>) :: Params a -> Params a -> Params a

sconcat :: NonEmpty (Params a) -> Params a

stimes :: Integral b => b -> Params a -> Params a

Monoid (Params a)

Methods

mempty :: Params a

mappend :: Params a -> Params a -> Params a

mconcat :: [Params a] -> Params a

Default (Params ())

Maps to unit.

Methods

def :: Params ()

(Default (Value a1), Default (Value a2)) => Default (Params (a1, a2))

Methods

def :: Params (a1, a2)

(Default (Value a1), Default (Value a2), Default (Value a3)) => Default (Params (a1, a2, a3))

Methods

def :: Params (a1, a2, a3)

(Default (Value a1), Default (Value a2), Default (Value a3), Default (Value a4)) => Default (Params (a1, a2, a3, a4))

Methods

def :: Params (a1, a2, a3, a4)

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

Methods

def :: Params (a1, a2, a3, a4, a5)

Default (Value a) => Default (Params (Identity a))

Methods

def :: Params (Identity a)

unit :: Params ()

Encode no parameters.

param :: Value a -> Params a

Lift an individual value encoder to a parameters encoder.

nullableParam :: Value a -> Params (Maybe a)

Lift an individual nullable value encoder to a parameters encoder.

Value

data Value a

An individual value encoder. Will be mapped to a single placeholder in the query.

Instances

Contravariant Value

Methods

contramap :: (a -> b) -> Value b -> Value a

(>$) :: b -> Value b -> Value a

Default (Value Bool)

Maps to bool.

Methods

def :: Value Bool

Default (Value Char)

Maps to char.

Methods

def :: Value Char

Default (Value Double)

Maps to float8.

Methods

def :: Value Double

Default (Value Float)

Maps to float4.

Methods

def :: Value Float

Default (Value Int16)

Maps to int2.

Methods

def :: Value Int16

Default (Value Int32)

Maps to int4.

Methods

def :: Value Int32

Default (Value Int64)

Maps to int8.

Methods

def :: Value Int64

Default (Value (TimeOfDay, TimeZone))

Maps to timetz.

Methods

def :: Value (TimeOfDay, TimeZone)

Default (Value ByteString)

Maps to bytea.

Methods

def :: Value ByteString

Default (Value Scientific)

Maps to numeric.

Methods

def :: Value Scientific

Default (Value Text)

Maps to text.

Methods

def :: Value Text

Default (Value UTCTime)

Maps to timestamptz.

Methods

def :: Value UTCTime

Default (Value Value)

Maps to json.

Methods

def :: Value Value

Default (Value UUID)

Maps to uuid.

Methods

def :: Value UUID

Default (Value Day)

Maps to date.

Methods

def :: Value Day

Default (Value DiffTime)

Maps to interval.

Methods

def :: Value DiffTime

Default (Value TimeOfDay)

Maps to time.

Methods

def :: Value TimeOfDay

Default (Value LocalTime)

Maps to timestamp.

Methods

def :: Value LocalTime

bool :: Value Bool

Encoder of BOOL values.

int2 :: Value Int16

Encoder of INT2 values.

int4 :: Value Int32

Encoder of INT4 values.

int8 :: Value Int64

Encoder of INT8 values.

float4 :: Value Float

Encoder of FLOAT4 values.

float8 :: Value Double

Encoder of FLOAT8 values.

numeric :: Value Scientific

Encoder of NUMERIC values.

char :: Value Char

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

text :: Value Text

Encoder of TEXT values.

bytea :: Value ByteString

Encoder of BYTEA values.

date :: Value Day

Encoder of DATE values.

timestamp :: Value LocalTime

Encoder of TIMESTAMP values.

timestamptz :: Value UTCTime

Encoder of TIMESTAMPTZ values.

time :: Value TimeOfDay

Encoder of TIME values.

timetz :: Value (TimeOfDay, TimeZone)

Encoder of TIMETZ values.

interval :: Value DiffTime

Encoder of INTERVAL values.

uuid :: Value UUID

Encoder of UUID values.

inet :: Value (NetAddr IP)

Encoder of INET values.

json :: Value Value

Encoder of JSON values from JSON AST.

jsonBytes :: Value ByteString

Encoder of JSON values from raw JSON.

jsonb :: Value Value

Encoder of JSONB values from JSON AST.

jsonbBytes :: Value ByteString

Encoder of JSONB values from raw JSON.

array :: Array a -> Value a

Unlifts the Array encoder to the plain Value encoder.

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

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

unknown :: Value ByteString

Identifies the value with the PostgreSQL's "unknown" type, thus leaving it up to Postgres to infer the actual type of the value.

The value transimitted is any value encoded in the Postgres' Text data format. For reference, see the Formats and Format Codes section of the Postgres' documentation.

Array

data Array a

A generic array encoder.

Here's an example of its usage:

x :: Value [[Int64]]
x =
  array (dimension foldl' (dimension foldl' (element int8)))

Please note that the PostgreSQL IN keyword does not "accept" an array, but rather a syntactical list of values, thus this encoder is not suited for that. Use a **field** = ANY($1) query instead.

element :: Value a -> Array a

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

nullableElement :: Value a -> Array (Maybe a)

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

dimension :: (forall a. (a -> b -> a) -> a -> c -> a) -> Array b -> Array c

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

Accepts:

• An implementation of the left-fold operation, such as Data.Foldable.foldl', which determines the input value.
• A component encoder, which can be either another dimension, element or nullableElement.

Insert Many

It is not currently possible to pass in an array of encodable values to use in an 'insert many' statement using Hasql. Instead, PostgreSQL's (9.4 or later) unnest function can be used to in an analogous way to haskell's zip function by passing in multiple arrays of values to be zipped into the rows we want to insert:

  insertMultipleLocations :: Statement (Vector (UUID, Double, Double)) ()
  insertMultipleLocations =
    statement sql encoder decoder True
    where
      sql =
        "insert into location (id, x, y) select * from unnest ($1, $2, $3)"
      encoder =
        contramap Vector.unzip3 $
        contrazip3 (vector Encoders.uuid) (vector Encoders.float8) (vector Encoders.float8)
        where
          vector value =
            Encoders.value (Encoders.array (Encoders.dimension foldl' (Encoders.element value)))
      decoder =
        Decoders.unit