deriving-aeson
Type driven generic aeson instance customisation
| LTS Haskell 23.4: | 0.2.10 |
| Stackage Nightly 2025-01-16: | 0.2.10 |
| Latest on Hackage: | 0.2.10 |
Maintained by [email protected]
This version can be pinned in stack with:
deriving-aeson-0.2.10@sha256:c6f2725d437f352c3267165575c756d18fbb16c1125d3263e3516e6a39098c10,1306Module documentation for 0.2.10
- Deriving
Depends on 2 packages(full list with versions):
deriving-aeson
This package provides a newtype wrapper where you can customise aeson’s generic methods using a type-level interface, which synergises well with DerivingVia.
{-# LANGUAGE DerivingVia, DataKinds, DeriveGeneric #-}
import Data.Aeson
import Deriving.Aeson
import qualified Data.ByteString.Lazy.Char8 as BL
data User = User
{ userId :: Int
, userName :: String
, userAPIToken :: Maybe String
} deriving Generic
deriving (FromJSON, ToJSON)
via CustomJSON '[OmitNothingFields, FieldLabelModifier '[StripPrefix "user", CamelToSnake]] User
testData :: [User]
testData = [User 42 "Alice" Nothing, User 43 "Bob" (Just "xyz")]
main = BL.putStrLn $ encode testData
-- [{"name":"Alice","id":42},{"api_token":"xyz","name":"Bob","id":43}]
Deriving.Aeson.Stock contains some aliases for even less boilerplates.
Prefixed str=CustomJSON '[FieldLabelModifier (StripPrefix str)]PrefixedSnake str=CustomJSON '[FieldLabelModifier (StripPrefix str, CamelToSnake)]Suffixed str=CustomJSON '[FieldLabelModifier (StripSuffix str)]SuffixedSnake str=CustomJSON '[FieldLabelModifier (StripSuffix str, CamelToSnake)]Snake=CustomJSON '[FieldLabelModifier '[StripPrefix str, CamelToSnake]]Vanilla=CustomJSON '[]
How it works
The wrapper type has a phantom type parameter t, a type-level builder of an Option.
Type-level primitives are reduced to one Option by the AesonOptions class.
newtype CustomJSON t a = CustomJSON { unCustomJSON :: a }
class AesonOptions xs where
aesonOptions :: Options
instance AesonOptions xs => AesonOptions (OmitNothingFields ': xs) where
aesonOptions = (aesonOptions @xs) { omitNothingFields = True }
...
You can use any (static) function for name modification by adding an instance of StringModifier.
data ToLower
instance StringModifier ToLower where
getStringModifier "" = ""
getStringModifier (c : xs) = toLower c : xs
Previous studies
- Type-driven safe derivation of ToJSON and FromJSON, using DerivingVia in GHC 8.6 and some type-level hacks
- Strip prefices from JSON representation