Hasql.Statement

Documentation

data Statement a b

A specification of a strictly single-statement query, which can be parameterized and prepared.

Consists of the following:

• SQL template,
• params encoder,
• result decoder,
• a flag, determining whether it should be prepared.

The SQL template must be formatted according to Postgres' standard, with any non-ASCII characters of the template encoded using UTF-8. According to the format, parameters must be referred to using the positional notation, as in the following: $1, $2, $3 and etc. Those references must be used to refer to the values of the Params encoder.

Following is an example of the declaration of a prepared statement with its associated codecs.

selectSum :: Hasql.Statement.Statement (Int64, Int64) Int64
selectSum =
  Hasql.Statement.Statement sql encoder decoder True
  where
    sql =
      "select ($1 + $2)"
    encoder =
      contramap fst (Hasql.Encoders.value Hasql.Encoders.int8) <>
      contramap snd (Hasql.Encoders.value Hasql.Encoders.int8)
    decoder =
      Hasql.Decoders.singleRow (Hasql.Decoders.value Hasql.Decoders.int8)

The statement above accepts a product of two parameters of type Int64 and produces a single result of type Int64.

Constructors

Statement ByteString (Params a) (Result b) Bool

Instances

Profunctor Statement

Methods

dimap :: (a -> b) -> (c -> d) -> Statement b c -> Statement a d

lmap :: (a -> b) -> Statement b c -> Statement a c

rmap :: (b -> c) -> Statement a b -> Statement a c

(#.) :: Coercible * c b => (b -> c) -> Statement a b -> Statement a c

(.#) :: Coercible * b a => Statement b c -> (a -> b) -> Statement a c

Functor (Statement a)

Methods

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

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