A layer around the deriving-aeson package, with the ability to strip one or more fields from the JSON output, and recover them when decoding using some specified defaults.
Because an example speaks more than a thousand words, let's start by having
a look at this Main module:
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE DerivingVia #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TypeApplications #-}
module Main where
import Data.Aeson
import Data.Set (Set)
import Data.Text (Text)
import Deriving.Aeson.Stripped
newtype WrappedInt
= WrappedInt Int
deriving newtype (FromJSON, Num, Show, ToJSON)
data RecordTest = RecordTest
{ testBool :: !Bool
, testNumber :: !Int
, testNewtype :: !WrappedInt
, testString :: !String
, testIsString :: !Text
, testList :: ![Int]
, testIsList :: !(Set Int)
, testMonoid :: !Ordering
, testValue :: !Double
}
deriving (Generic, Show)
deriving (FromJSON, ToJSON)
via StrippedJSON
'[ RField "testBool" 'False
, RField "testNumber" 7
, RField "testNewtype" (Coerce 42 Int)
, RField "testString" "string"
, RField "testIsString" (FromString "text")
, RField "testList" '[ 10, 11, 12 ]
, RField "testIsList" (FromList '[ 13, 14, 13 ])
, RField "testMonoid" Mempty
]
'[ FieldLabelModifier CamelToSnake
]
RecordTest
main :: IO ()
main = do
let output = encode $ RecordTest True 1 2 "s" "t" [1..3] (fromList [4..6]) GT 3.14
putStrLn "# Stripping fields:"
print output
putStrLn "# And recovering them later:"
print $ decode @RecordTest outputUpon running the corresponding executable, you should get this output :
# Stripping fields:
"{\"test_value\":3.14}"
# And recovering them later:
Just (RecordTest {testBool = False, testNumber = 7, testNewtype = 42, testString = "string", testIsString = "text", testList = [10,11,12], testIsList = fromList [13,14], testMonoid = EQ, testValue = 3.14})
This package revolves entirely around the
StrippedJSON
newtype, which takes two type parameters:
-
a list of instructions indicating which fields should be removed, and how they should be recovered:
Instruction Use for Field identifier RFieldrecord values name CFieldnon-record single-constructor values zero-based position Each instruction takes a field identifier and a default value used to recover the field when decoding.
See the
RecoverableValueinstances for examples of what can be used as default values. Or don't hesitate to roll your own! (PRs welcome!) -
a list of
AesonOptionsindicating how to customize the JSON output.This works exactly the same as the only parameter to
CustomJSONfrom the deriving-aeson package.
The Haddock documentation for the package is available here.
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