module Data.Aeson.Transform ( -- * Example usage -- $use -- * Transformation builder Builder(..) -- * Executing transformation , transform ) where import Data.Aeson as A import Data.Text import qualified Data.Vector as Vec import qualified Data.HashMap.Strict as H -- | Transformations are specified by creating 'Builder' instances. -- Builders specify how to navigate through input JSON and construct -- output at various nodes in the tree. -- data Builder = Id -- ^ Pass input directly as output | At Text Builder -- ^ Move to value in current object | Attr Text -- ^ Get value in current object | Attrs [Text] -- ^ Filter current object by keys | Map Builder -- ^ Map over input array | Index Int Builder -- ^ Get value at index of current array | Obj (H.HashMap Text Builder) -- ^ Produce object with given keys -- | Generates new Aeson 'Value' guided by a 'Builder' -- transform :: Builder -> Value -> Value transform (At k b) (A.Object o) = transform b $ o H.! k transform (At _ _) _ = error "Expecting object (At)" transform (Index i b) (Array a) = transform b $ a Vec.! i transform (Index _ _) _ = error "Expecting array (Index)" transform (Map b) (Array a) = Array $ Vec.map (transform b) a transform (Map _) _ = error "Expecting array (Map)" transform (Attr k) (A.Object o) = o H.! k transform (Attr _) _ = error "Expecting object (Attr)" transform (Attrs ks) (A.Object o) = A.Object $ H.filterWithKey (const . (`elem` ks)) o transform (Attrs _) _ = error "Expecting object (Attrs)" transform (Obj fs) x = A.Object $ H.map (`transform` x) fs transform Id x = x -- $use -- -- Filter unwanted attributes from an object -- -- > Attrs ["nice", "good"] -- > -- > -- { bad: 3, good: 1, nice: 500, evil: -3 } -- > -- => { good: 1, nice: 500 } -- -- Grab value -- -- > Attr "foo" -- > -- > -- { foo: 2 } => 2 -- -- Dig deeper -- -- > At "foo" $ Attr "bar" -- > -- > -- { foo: { bar: 3 }} => 3 -- -- Map stuff -- -- > Map $ Attr "foo" -- > -- > -- [{ foo:1, foo:2 }] => [1, 2] -- -- Extract indices -- -- > Map $ Index 0 Id -- > -- > -- [[1,2], [3,4]] => [1, 3] -- -- Create object -- -- > Obj $ fromList [ -- > ("first", Index 0 Id) -- > , ("second", Index 1 Id) -- > ] -- > -- > -- ["hi", "bye"] => { first:"hi", second:"bye" }