[英]Haskell Aeson nested array JSON
I have trouble parsing the Tag in the following JSON structure. 我无法解析以下JSON结构中的Tag。 The parser works only when i declare it to be
tags :: !Array
It fails when i declare it as tags :: [Tag]
解析器仅在我将其声明为
tags :: !Array
时起作用,而在我将其声明为tags :: [Tag]
时失败
Why? 为什么?
{
"response": {
"status": "ok",
"results": [
{
"type": "article",
"fields": {
"wordcount": "497"
},
"tags": [
{
"id": "profile/barryglendenning"
}
]
}
]
}
}
data Field = Field{
wordcount :: Int
} deriving (Show)
instance FromJSON Field where
parseJSON (Object o) = Field <$> (o .: "wordcount")
parseJSON _ = mzero
data Tag = Tag{
id :: Text
} deriving (Show)
instance FromJSON Tag where
parseJSON (Object o) = Tag <$> (o .: "id")
parseJSON _ = mzero
data SearchResult = SearchResult {
type:: Text,
field :: Field,
tags :: !Array
} deriving (Show)
instance FromJSON SearchResult where
parseJSON (Object o) = do
let t1 = o .: "type"
let t2 = o .: "fields"
let t3 = o .: "tags"
SearchResult <$> t1 <*> t2 <*> t3
parseJSON _ = mzero
data ContentrResult = ContentrResult {
results :: [SearchResult],
status :: Text
} deriving (Show)
instance FromJSON ContentrResult where
parseJSON (Object o) = do
r <- o .: "response"
ContentrResult <$> r .: "results"
<*> r .: "status"
parseJSON _ = mzero
Nothing
isn't a very useful for debugging is it? Nothing
对调试不是很有用的吗?
I managed to get your example JSON parsing the tags
as a [Tag]
. 我设法让您的示例JSON将
tags
解析为[Tag]
。 I wonder if your error could be related to the wordcount
field being a String
in the JSON rather than a Number
. 我想知道您的错误是否可能与
wordcount
字段是JSON中的String
而不是Number
。
Here is a more-or-less self-contained example where I changed the example JSON wordcount to a number: 这是一个或多或少独立的示例,其中我将示例JSON wordcount更改为数字:
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE QuasiQuotes #-}
module Main where
import Lib (str)
import Control.Monad (mzero)
import Data.Aeson
import qualified Data.ByteString.Lazy.Char8 as LBSC
import Data.Text
data Field = Field {
wordcount :: Int
} deriving (Show)
instance FromJSON Field where
parseJSON (Object o) = Field <$> o .: "wordcount"
parseJSON _ = mzero
data Tag = Tag {
id :: Text
} deriving (Show)
instance FromJSON Tag where
parseJSON (Object o) = Tag <$> (o .: "id")
parseJSON _ = mzero
data SearchResult = SearchResult {
typ :: Text,
fields :: Field,
tags :: [Tag]
} deriving (Show)
instance FromJSON SearchResult where
parseJSON (Object v) = SearchResult <$> v .: "type" <*> v .: "fields" <*> v .: "tags"
parseJSON _ = mzero
data ContentrResult = ContentrResult {
results :: [SearchResult],
status :: Text
} deriving (Show)
instance FromJSON ContentrResult where
parseJSON (Object v) = ContentrResult <$> v.: "results" <*> v .: "status"
parseJSON _ = mzero
data Response = Response {
response :: ContentrResult
} deriving (Show)
instance FromJSON Response where
parseJSON (Object v) = Response <$> v .: "response"
parseJSON _ = mzero
responseJson :: String
responseJson = [str|
{
"response": {
"status": "ok",
"results": [
{
"type": "article",
"fields": {
"wordcount": 497
},
"tags": [
{
"id": "profile/barryglendenning"
}
]
}
]
}
}
|]
main :: IO ()
main = do
print r
putStrLn ""
where
r :: Maybe Response
r = decode (LBSC.pack responseJson)
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