Reference + Entity = Refty ♡

Formatted JSON generator for API server inspired by normalizr.

We will generate json like:

{
  "entities": {
    "users": {
      "1": { "id": 1, "name": "Lelouch" },
      "2": { "id": 2, "name": "Suzaku" },
      "3": { "id": 3, "name": "Jeremiah" }
    },
    "comments": {
      "1": { "id": 1, "body": "Hello", "userId": 1 },
      "4": { "id": 4, "body": "Foo", "userId": 1 },
      "2": { "id": 2, "body": "World", "userId": 1 },
      "3": { "id": 3, "body": ":)", "userId": 3 }
    }
  },
  "references": {
    "self": [ 2, 1, 3 ],
    "userComments": { "1": [ 1, 4, 2 ], "3": [ 3 ] }
  }
}

First, define data types like:

User.hs:

import Data.Aeson
import Data.Text as T
import GHC.Generics (Generic)

data User = User
  { id :: Int
  , name :: T.Text
  } deriving (Generic, Show)

instance ToJSON User

Comment.hs:

import Data.Aeson
import Data.Text as T
import GHC.Generics (Generic)

data Comment = Comment
  { id :: Int
  , userId :: Int
  , body :: T.Text
  } deriving (Generic, Show)

instance ToJSON Comment

Next, create JSON.

import Data.Aeson
import Refty
import qualified User as U
import qualified Comment as C

-- Sample data
users =
  [ U.User 2 "Suzaku"
  , U.User 1 "Lelouch"
  , U.User 3 "Jeremiah"
  ]

comments =
  [ C.Comment 1 1 "Hello"
  , C.Comment 4 1 "Foo"
  , C.Comment 2 1 "World"
  , C.Comment 3 3 ":)"
  ]

encode $ refty
  [ builder (resource "users" U.id $ listEntity users) [ selfRef "self" ]
  , builder (resource "comments" C.id $ listEntity comments) [ hasManyRef "userComments" C.userId ]
  ]