server: add _is_null operator, closes #106

server/src-lib/Hasura/GraphQL/Resolve/BoolExp.hs

@@ -1,7 +1,8 @@
-{-# LANGUAGE FlexibleContexts  #-}
-{-# LANGUAGE MultiWayIf        #-}
-{-# LANGUAGE NoImplicitPrelude #-}
-{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE FlexibleContexts      #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE MultiWayIf            #-}
+{-# LANGUAGE NoImplicitPrelude     #-}
+{-# LANGUAGE OverloadedStrings     #-}
 
 module Hasura.GraphQL.Resolve.BoolExp
   ( parseBoolExp
@@ -25,6 +26,7 @@ import           Hasura.GraphQL.Validate.Types
 import           Hasura.RQL.Types
 
 import           Hasura.SQL.Types
+import           Hasura.SQL.Value
 
 parseOpExps
   :: (MonadError QErr m, MonadReader r m, Has FieldMap r)
@@ -35,6 +37,7 @@ parseOpExps annVal = do
       "_eq"       -> fmap RA.AEQ <$> asPGColValM v
       "_ne"       -> fmap RA.ANE <$> asPGColValM v
       "_neq"      -> fmap RA.ANE <$> asPGColValM v
+      "_is_null"  -> resolveIsNull v
 
       "_in"       -> fmap (RA.AIN . catMaybes) <$> parseMany asPGColValM v
       "_nin"      -> fmap (RA.ANIN . catMaybes) <$> parseMany asPGColValM v
@@ -59,6 +62,13 @@ parseOpExps annVal = do
           <> ": "
           <> showName k
   return $ map RA.OEVal $ catMaybes $ fromMaybe [] opExpsM
+  where
+    resolveIsNull v = case v of
+      AGScalar _ Nothing -> return Nothing
+      AGScalar _ (Just (PGValBoolean b)) ->
+        return $ Just $ bool RA.ANISNOTNULL RA.ANISNULL b
+      AGScalar _ _ -> throw500 "boolean value is expected"
+      _ -> tyMismatch "pgvalue" v
 
 parseColExp
   :: (MonadError QErr m, MonadReader r m, Has FieldMap r)

server/src-lib/Hasura/GraphQL/Schema.hs

@@ -31,9 +31,9 @@ import qualified Language.GraphQL.Draft.Syntax  as G
 import           Hasura.GraphQL.Resolve.Context
 import           Hasura.GraphQL.Validate.Types
 
+import           Hasura.Prelude
 import           Hasura.RQL.Types
 import           Hasura.SQL.Types
-import           Hasura.Prelude
 
 import qualified Hasura.SQL.DML                 as S
 
@@ -116,6 +116,7 @@ mkCompExpInp colTy =
   [ map (mk colScalarTy) typedOps
   , map (mk $ G.toLT colScalarTy) listOps
   , bool [] (map (mk $ mkScalarTy PGText) stringOps) isStringTy
+  , [InpValInfo Nothing "_is_null" $ G.TypeNamed $ G.NamedType "Boolean"]
   ]
   where
     tyDesc = mconcat

server/src-lib/Hasura/RQL/GBoolExp.hs

@@ -1,9 +1,9 @@
-{-# LANGUAGE FlexibleContexts     #-}
-{-# LANGUAGE FlexibleInstances    #-}
-{-# LANGUAGE LambdaCase           #-}
-{-# LANGUAGE MultiWayIf           #-}
-{-# LANGUAGE OverloadedStrings    #-}
-{-# LANGUAGE TypeSynonymInstances #-}
+{-# LANGUAGE FlexibleContexts      #-}
+{-# LANGUAGE FlexibleInstances     #-}
+{-# LANGUAGE LambdaCase            #-}
+{-# LANGUAGE MultiWayIf            #-}
+{-# LANGUAGE OverloadedStrings     #-}
+{-# LANGUAGE TypeSynonymInstances  #-}
 
 module Hasura.RQL.GBoolExp where
 
@@ -40,6 +40,9 @@ data AnnValOpExpG a
   | ASIMILAR !a -- similar, regex
   | ANSIMILAR !a-- not similar, regex
 
+  | ANISNULL -- IS NULL
+  | ANISNOTNULL -- IS NOT NULL
+
   deriving (Eq, Show)
 
 data OpExpG a
@@ -445,6 +448,8 @@ mkBoolExpBuilder rhsBldr lhs = \case
   ANILIKE val   -> mkSimpleBoolExpBuilder (S.BECompare S.SNILIKE) val
   ASIMILAR val  -> mkSimpleBoolExpBuilder (S.BECompare S.SSIMILAR) val
   ANSIMILAR val -> mkSimpleBoolExpBuilder (S.BECompare S.SNSIMILAR) val
+  ANISNULL      -> return $ S.BENull lhs
+  ANISNOTNULL   -> return $ S.BENotNull lhs
   where
     mkSimpleBoolExpBuilder beF pgColVal =
       beF lhs <$> rhsBldr pgColVal