如果啓用FlexibleInstances
,可以使實例[Person]
。你可以分析你的對象Map Text Value
,然後分析每個元素在地圖:
{-# LANGUAGE UnicodeSyntax, OverloadedStrings, FlexibleInstances #-}
module Person (
) where
import Data.Aeson
import Data.Aeson.Types
import Data.Text.Lazy
import Data.Text.Lazy.Encoding
import Data.Map (Map)
import qualified Data.Map as M
data Person = Person {
id ∷ Text,
name ∷ Text,
age ∷ Int }
deriving (Eq, Ord, Read, Show)
instance FromJSON [Person] where
parseJSON v = do
objs ← parseJSON v ∷ Parser (Map Text Value)
sequence [withObject "person"
(\v' → Person i <$> v' .: "name" <*> v' .: "age") obj |
(i, obj) ← M.toList objs]
test ∷ Text
test = "{\"bob_id\":{\"name\":\"bob\",\"age\":20},\"jack_id\":{\"name\":\"jack\",\"age\":25}}"
res ∷ Maybe [Person]
res = decode (encodeUtf8 test)
爲什麼不可能?只是將結果解析爲「摺疊」以將其轉換爲「[Person]」?但我從未使用過'aeson'。也許說明問題更清楚。 – jakubdaniel