Add deriveFromGraphQL

For deriving FromGraphQL instances automatically.

tests/Language/GraphQL/ClassSpec.hs

@@ -12,16 +12,22 @@ import Data.Text (Text)
 import Data.Time (UTCTime(..))
 import Data.Time.Calendar.OrdinalDate (fromOrdinalDate)
 import qualified Language.GraphQL.Type as Type
-import Language.GraphQL.Class (FromGraphQL(..), ToGraphQL(..), deriveToGraphQL)
+import Language.GraphQL.Class
+    ( FromGraphQL(..)
+    , ToGraphQL(..)
+    , deriveFromGraphQL
+    , deriveToGraphQL
+    )
 import Test.Hspec (Spec, describe, it, shouldBe)
 import qualified Data.HashMap.Strict as HashMap
 
 data TwoFieldRecord = TwoFieldRecord
     { x :: Int
     , y :: Bool
-    }
+    } deriving (Eq, Show)
 
 $(deriveToGraphQL ''TwoFieldRecord)
+$(deriveFromGraphQL ''TwoFieldRecord)
 
 spec :: Spec
 spec = do
@@ -76,7 +82,7 @@ spec = do
              in actual `shouldBe` expected
 
     describe "deriveToGraphQL" $ do
-        it "derives ToGraphQL for a record" $ do
+        it "derives ToGraphQL for a record with multiple fields" $ do
             let expected = Type.Object $ HashMap.fromList
                     [ ("x", Type.Int 1)
                     , ("y", Type.Boolean True)
@@ -87,3 +93,15 @@ spec = do
                     , y = True
                     }
              in toGraphQL given `shouldBe` expected
+
+    describe "deriveFromGraphQL" $ do
+        it "derives FromGraphQL for a record with multiple fields" $ do
+            let given = Type.Object $ HashMap.fromList
+                    [ ("x", Type.Int 1)
+                    , ("y", Type.Boolean True)
+                    ]
+                expected = TwoFieldRecord
+                    { x = 1
+                    , y = True
+                    }
+             in fromGraphQL given `shouldBe` Just expected