elm-export helpers for Persistent Entities.
newtype Ent (field :: Symbol) a = Ent (Entity a)
deriving (Generic)
type EntId a = Ent "id" a
Ent is a newtype that wraps Persistent Entity's, allowing you to export them to
Elm types. Specifically, it adds a {To,From}JSON instance which adds an id
field, as well as an ElmType
instance that adds an id
field constructor.
Let's define a Persistent model:
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE QuasiQuotes #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE StandaloneDeriving #-}
module Main where
import Data.Aeson
import Data.Text
import Database.Persist.TH
import Elm
import GHC.Generics
import Elm.Export.Persist
import Elm.Export.Persist.BackendKey ()
share [mkPersist sqlSettings, mkMigrate "migrateAccount"] [persistLowerCase|
Account
email Text
password Text
deriving Show Generic
UniqueEmail email
|]
instance ToJSON Account
instance FromJSON Account
instance ElmType Account
-- use GeneralizedNewtypeDeriving for ids
-- this picks a simpler int-encoding
deriving instance ElmType AccountId
Now let's export it with an id field:
module Main where
import Db
import Elm
import Data.Proxy
mkSpecBody :: ElmType a => a -> [Text]
mkSpecBody a =
[ toElmTypeSource a
, toElmDecoderSource a
, toElmEncoderSource a
]
defImports :: [Text]
defImports =
[ "import Json.Decode exposing (..)"
, "import Json.Decode.Pipeline exposing (..)"
, "import Json.Encode"
, "import Http"
, "import String"
]
accountSpec :: Spec
accountSpec =
Spec ["Generated", "Account"] $
defImports ++ mkSpecBody (Proxy :: Proxy (EntId Account))
main :: IO ()
main = specsToDir [accountSpec] "some/where/output"
This generates:
module Generated.Account exposing (..)
import Json.Decode exposing (..)
import Json.Decode.Pipeline exposing (..)
import Json.Encode
import Http
import String
type alias Account =
{ accountEmail : String
, accountPassword : String
, id : Int
}
decodeAccount : Decoder Account
decodeAccount =
decode Account
|> required "accountEmail" string
|> required "accountPassword" string
|> required "id" int
encodeAccount : Account -> Json.Encode.Value
encodeAccount x =
Json.Encode.object
[ ( "accountEmail", Json.Encode.string x.accountEmail )
, ( "accountPassword", Json.Encode.string x.accountPassword )
, ( "id", Json.Encode.int x.id )
]