mirror of
https://github.com/nikita-volkov/hasql.git
synced 2024-11-25 06:33:19 +03:00
120 lines
4.6 KiB
Haskell
120 lines
4.6 KiB
Haskell
module Hasql.Statement
|
|
( Statement (..),
|
|
refineResult,
|
|
|
|
-- * Recipies
|
|
|
|
-- ** Insert many
|
|
-- $insertMany
|
|
|
|
-- ** IN and NOT IN
|
|
-- $inAndNotIn
|
|
)
|
|
where
|
|
|
|
import qualified Hasql.Decoders as Decoders
|
|
import qualified Hasql.Encoders as Encoders
|
|
import qualified Hasql.Private.Decoders as Decoders
|
|
import Hasql.Private.Prelude
|
|
|
|
-- |
|
|
-- 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 a positional notation, as in the following:
|
|
-- @$1@, @$2@, @$3@ and etc.
|
|
-- Those references must be used in accordance with the order in which
|
|
-- the value encoders are specified in 'Encoders.Params'.
|
|
--
|
|
-- Following is an example of a declaration of a prepared statement with its associated codecs.
|
|
--
|
|
-- @
|
|
-- selectSum :: 'Statement' (Int64, Int64) Int64
|
|
-- selectSum = 'Statement' sql encoder decoder True where
|
|
-- sql = "select ($1 + $2)"
|
|
-- encoder =
|
|
-- ('fst' '>$<' Encoders.'Hasql.Encoders.param' (Encoders.'Hasql.Encoders.nonNullable' Encoders.'Hasql.Encoders.int8')) '<>'
|
|
-- ('snd' '>$<' Encoders.'Hasql.Encoders.param' (Encoders.'Hasql.Encoders.nonNullable' Encoders.'Hasql.Encoders.int8'))
|
|
-- decoder = Decoders.'Hasql.Decoders.singleRow' (Decoders.'Hasql.Decoders.column' (Decoders.'Hasql.Decoders.nonNullable' Decoders.'Hasql.Decoders.int8'))
|
|
-- @
|
|
--
|
|
-- The statement above accepts a product of two parameters of type 'Int64'
|
|
-- and produces a single result of type 'Int64'.
|
|
data Statement a b
|
|
= Statement ByteString (Encoders.Params a) (Decoders.Result b) Bool
|
|
|
|
instance Functor (Statement a) where
|
|
{-# INLINE fmap #-}
|
|
fmap = rmap
|
|
|
|
instance Profunctor Statement where
|
|
{-# INLINE dimap #-}
|
|
dimap f1 f2 (Statement template encoder decoder preparable) =
|
|
Statement template (contramap f1 encoder) (fmap f2 decoder) preparable
|
|
|
|
-- |
|
|
-- Refine a result of a statement,
|
|
-- causing the running session to fail with the `UnexpectedResult` error in case of refinement failure.
|
|
--
|
|
-- This function is especially useful for refining the results of statements produced with
|
|
-- <http://hackage.haskell.org/package/hasql-th the \"hasql-th\" library>.
|
|
refineResult :: (a -> Either Text b) -> Statement params a -> Statement params b
|
|
refineResult refiner (Statement template encoder decoder preparable) =
|
|
Statement template encoder (Decoders.refineResult refiner decoder) preparable
|
|
|
|
-- $insertMany
|
|
--
|
|
-- It is not currently possible to pass in an array of encodable values
|
|
-- to use in an insert many statement. Instead, PostgreSQL's
|
|
-- (9.4 or later) @unnest@ function can be used 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.'Data.Vector.unzip3' $
|
|
-- contrazip3 (vector Encoders.'Encoders.uuid') (vector Encoders.'Encoders.float8') (vector Encoders.'Encoders.float8')
|
|
-- where
|
|
-- vector =
|
|
-- Encoders.'Encoders.param' .
|
|
-- Encoders.'Encoders.nonNullable' .
|
|
-- Encoders.'Encoders.array' .
|
|
-- Encoders.'Encoders.dimension' 'foldl'' .
|
|
-- Encoders.'Encoders.element' .
|
|
-- Encoders.'Encoders.nonNullable'
|
|
-- decoder = Decoders.'Decoders.noResult'
|
|
-- @
|
|
--
|
|
-- This approach is much more efficient than executing a single-row Insert
|
|
-- statement multiple times.
|
|
|
|
-- $inAndNotIn
|
|
--
|
|
-- There is a common misconception that Postgresql supports array
|
|
-- as a parameter for the @IN@ operator.
|
|
-- However Postgres only supports a syntactical list of values with it,
|
|
-- i.e., you have to specify each option as an individual parameter
|
|
-- (@something IN ($1, $2, $3)@).
|
|
--
|
|
-- Clearly it would be much more convenient to provide an array as a single parameter,
|
|
-- but the @IN@ operator does not support that.
|
|
-- Fortunately, Postgres does provide such functionality with other operators:
|
|
--
|
|
-- * Use @something = ANY($1)@ instead of @something IN ($1)@
|
|
-- * Use @something <> ALL($1)@ instead of @something NOT IN ($1)@
|
|
--
|
|
-- For details see
|
|
-- <https://www.postgresql.org/docs/9.6/static/functions-comparisons.html#AEN20944 the Postgresql docs>.
|