deriving-aeson: Type driven generic aeson instance customisation
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This package provides a newtype wrapper with FromJSON/ToJSON instances customisable via a phantom type parameter. The instances can be rendered to the original type using DerivingVia.
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| Versions | 0, 0.1, 0.1.1, 0.1.2, 0.2, 0.2.1, 0.2.2, 0.2.3, 0.2.4, 0.2.5, 0.2.6, 0.2.6.1, 0.2.7, 0.2.8, 0.2.8, 0.2.9 |
|---|---|
| Change log | CHANGELOG.md |
| Dependencies | aeson (>=1.4.7.0 && <2.1), base (>=4.12 && <5) [details] |
| License | BSD-3-Clause |
| Copyright | Copyright (c) 2020 Fumiaki Kinoshita |
| Author | Fumiaki Kinoshita |
| Maintainer | fumiexcel@gmail.com |
| Category | JSON, Generics |
| Bug tracker | https://github.com/fumieval/deriving-aeson |
| Source repo | head: git clone https://github.com/fumieval/deriving-aeson.git |
| Uploaded | by FumiakiKinoshita at 2021-11-10T11:21:22Z |
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[back to package description]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)]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