| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Data.HighJson.TH
- deriveJsonSwagger :: Name -> Name -> Q [Dec]
- jsonSerializer :: AllHave ToJSON as => HighSpec a ty as -> a -> Value
- jsonEncoder :: AllHave ToJSON as => HighSpec a ty as -> a -> Encoding
- jsonParser :: AllHave FromJSON as => HighSpec a ty as -> Value -> Parser a
- makeDeclareNamedSchema :: (AllHave ToSchema ts, AllHave ToJSON ts, IsValidSwaggerType ty ts) => HighSpec k ty ts -> f k -> DeclM NamedSchema
- class ToSchema a where
- class ToJSON a where
- class FromJSON a where
Documentation
makeDeclareNamedSchema :: (AllHave ToSchema ts, AllHave ToJSON ts, IsValidSwaggerType ty ts) => HighSpec k ty ts -> f k -> DeclM NamedSchema #
Automatically generate a NamedSchema from a HighSpec
Convert a type into Schema
An example type and instance:
{-# LANGUAGE OverloadedStrings #-} -- allows to write Text literals
{-# LANGUAGE OverloadedLists #-} -- allows to write Map and HashMap as lists
import Control.Lens
data Coord = Coord { x :: Double, y :: Double }
instance ToSchema Coord where
declareNamedSchema = do
doubleSchema <- declareSchemaRef (Proxy :: Proxy Double)
return $ NamedSchema (Just "Coord")) $ mempty
& type_ .~ SwaggerObject
& properties .~
[ ("x", doubleSchema)
, ("y", doubleSchema)
]
& required .~ [ "x", "y" ]
Instead of manually writing your ToSchemadeclareNamedSchema
To do that, simply add deriving clause to your datatype
and declare a GenericToSchemadeclareNamedSchema
For instance, the previous example can be simplified into this:
{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics (Generic)
data Coord = Coord { x :: Double, y :: Double } deriving Generic
instance ToSchema Coord
Methods
declareNamedSchema :: proxy a -> Declare (Definitions Schema) NamedSchema #
Convert a type into an optionally named schema together with all used definitions. Note that the schema itself is included in definitions only if it is recursive (and thus needs its definition in scope).
Instances
A type that can be converted to JSON.
An example type and instance:
-- Allow ourselves to writeTextliterals. {-# LANGUAGE OverloadedStrings #-} data Coord = Coord { x :: Double, y :: Double } instance ToJSON Coord where toJSON (Coord x y) =object["x".=x, "y".=y] toEncoding (Coord x y) =pairs("x".=x<>"y".=y)
Instead of manually writing your ToJSON instance, there are two options
to do it automatically:
- Data.Aeson.TH provides Template Haskell functions which will derive an instance at compile time. The generated instance is optimized for your type so will probably be more efficient than the following two options:
- The compiler can provide a default generic implementation for
toJSON.
To use the second, simply add a deriving clause to your
datatype and declare a GenericToJSON instance for your datatype without giving
definitions for toJSON or toEncoding.
For example, the previous example can be simplified to a more minimal instance:
{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics
data Coord = Coord { x :: Double, y :: Double } deriving Generic
instance ToJSON Coord where
toEncoding = genericToEncoding defaultOptions
Why do we provide an implementation for toEncoding here? The
toEncoding function is a relatively new addition to this class.
To allow users of older versions of this library to upgrade without
having to edit all of their instances or encounter surprising
incompatibilities, the default implementation of toEncoding uses
toJSON. This produces correct results, but since it performs an
intermediate conversion to a Value, it will be less efficient
than directly emitting an Encoding. Our one-liner definition of
toEncoding above bypasses the intermediate Value.
If DefaultSignatures doesn't give exactly the results you want,
you can customize the generic encoding with only a tiny amount of
effort, using genericToJSON and genericToEncoding with your
preferred Options:
instance ToJSON Coord where
toJSON = genericToJSON defaultOptions
toEncoding = genericToEncoding defaultOptions
Methods
Convert a Haskell value to a JSON-friendly intermediate type.
toEncoding :: a -> Encoding #
Encode a Haskell value as JSON.
The default implementation of this method creates an
intermediate Value using toJSON. This provides
source-level compatibility for people upgrading from older
versions of this library, but obviously offers no performance
advantage.
To benefit from direct encoding, you must provide an
implementation for this method. The easiest way to do so is by
having your types implement Generic using the DeriveGeneric
extension, and then have GHC generate a method body as follows.
instance ToJSON Coord where
toEncoding = genericToEncoding defaultOptions
toJSONList :: [a] -> Value #
toEncodingList :: [a] -> Encoding #
Instances
A type that can be converted from JSON, with the possibility of failure.
In many cases, you can get the compiler to generate parsing code for you (see below). To begin, let's cover writing an instance by hand.
There are various reasons a conversion could fail. For example, an
Object could be missing a required key, an Array could be of
the wrong size, or a value could be of an incompatible type.
The basic ways to signal a failed conversion are as follows:
emptyandmzerowork, but are terse and uninformativefailyields a custom error messagetypeMismatchproduces an informative message for cases when the value encountered is not of the expected type
An example type and instance:
-- Allow ourselves to writeTextliterals. {-# LANGUAGE OverloadedStrings #-} data Coord = Coord { x :: Double, y :: Double } instance FromJSON Coord where parseJSON (Objectv) = Coord<$>v.:"x"<*>v.:"y" -- We do not expect a non-Objectvalue here. -- We could usemzeroto fail, buttypeMismatch-- gives a much more informative error message. parseJSON invalid =typeMismatch"Coord" invalid
Instead of manually writing your FromJSON instance, there are two options
to do it automatically:
- Data.Aeson.TH provides Template Haskell functions which will derive an instance at compile time. The generated instance is optimized for your type so will probably be more efficient than the following two options:
- The compiler can provide a default generic implementation for
parseJSON.
To use the second, simply add a deriving clause to your
datatype and declare a GenericFromJSON instance for your datatype without giving
a definition for parseJSON.
For example, the previous example can be simplified to just:
{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics
data Coord = Coord { x :: Double, y :: Double } deriving Generic
instance FromJSON Coord
If DefaultSignatures doesn't give exactly the results you want,
you can customize the generic decoding with only a tiny amount of
effort, using genericParseJSON with your preferred Options:
instance FromJSON Coord where
parseJSON = genericParseJSON defaultOptions
Instances