From 6d8b84c55c0121046f9e44b06cc730482f6d908d Mon Sep 17 00:00:00 2001
From: Felipe Lessa <felipe.lessa@gmail.com>
Date: Sun, 27 Jan 2013 17:28:00 -0200
Subject: [PATCH] valList [] now works.

---
 src/Database/Esqueleto/Internal/Sql.hs | 18 +++++++++++++-----
 test/Test.hs                           | 21 +++++++++++++++++++++
 2 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/src/Database/Esqueleto/Internal/Sql.hs b/src/Database/Esqueleto/Internal/Sql.hs
index 8d95e52..4f92c53 100644
--- a/src/Database/Esqueleto/Internal/Sql.hs
+++ b/src/Database/Esqueleto/Internal/Sql.hs
@@ -229,6 +229,7 @@ data SqlExpr a where
   EMaybe   :: SqlExpr a -> SqlExpr (Maybe a)
   ERaw     :: NeedParens -> (Connection -> (TLB.Builder, [PersistValue])) -> SqlExpr (Value a)
   EList    :: SqlExpr (Value a) -> SqlExpr (ValueList a)
+  EEmptyList :: SqlExpr (ValueList a)
   EOrderBy :: OrderByType -> SqlExpr (Value a) -> SqlExpr OrderBy
   ESet     :: (SqlExpr (Entity val) -> SqlExpr (Value ())) -> SqlExpr (Update val)
   EPreprocessedFrom :: a -> FromClause -> SqlExpr (PreprocessedFrom a)
@@ -299,7 +300,7 @@ instance Esqueleto SqlQuery SqlExpr SqlBackend where
 
   val = ERaw Never . const . (,) "?" . return . toPersistValue
 
-  isNothing (ERaw p f) = ERaw Never $ first ((<> " IS NULL") . parensM p) . f
+  isNothing (ERaw p f) = ERaw Parens $ first ((<> " IS NULL") . parensM p) . f
   just (ERaw p f) = ERaw p f
   nothing   = unsafeSqlValue "NULL"
   countRows = unsafeSqlValue "COUNT(*)"
@@ -328,11 +329,12 @@ instance Esqueleto SqlQuery SqlExpr SqlBackend where
   subList_select         = EList . sub_select
   subList_selectDistinct = EList . sub_selectDistinct
 
+  valList []   = EEmptyList
   valList vals = EList $ ERaw Parens $ const ( uncommas ("?" <$ vals)
                                              , map toPersistValue vals )
 
-  v `in_`   e = unsafeSqlBinOp     " IN " v (veryUnsafeCoerceSqlExprValueList e)
-  v `notIn` e = unsafeSqlBinOp " NOT IN " v (veryUnsafeCoerceSqlExprValueList e)
+  v `in_`   e = ifNotEmptyList e False $ unsafeSqlBinOp     " IN " v (veryUnsafeCoerceSqlExprValueList e)
+  v `notIn` e = ifNotEmptyList e True  $ unsafeSqlBinOp " NOT IN " v (veryUnsafeCoerceSqlExprValueList e)
 
   exists    = unsafeSqlFunction     "EXISTS " . existsHelper
   notExists = unsafeSqlFunction "NOT EXISTS " . existsHelper
@@ -374,6 +376,10 @@ existsHelper =
   flip (toRawSql SELECT) .
   (>> return (val True :: SqlExpr (Value Bool)))
 
+ifNotEmptyList :: SqlExpr (ValueList a) -> Bool -> SqlExpr (Value Bool) -> SqlExpr (Value Bool)
+ifNotEmptyList EEmptyList b _ = val b
+ifNotEmptyList (EList _)  _ x = x
+
 
 ----------------------------------------------------------------------
 
@@ -449,9 +455,11 @@ veryUnsafeCoerceSqlExprValue (ERaw p f) = ERaw p f
 
 
 -- | (Internal) Coerce a value's type from 'SqlExpr (ValueList
--- a)' to 'SqlExpr (Value a)'.
+-- a)' to 'SqlExpr (Value a)'.  Does not work with empty lists.
 veryUnsafeCoerceSqlExprValueList :: SqlExpr (ValueList a) -> SqlExpr (Value a)
-veryUnsafeCoerceSqlExprValueList (EList v) = v
+veryUnsafeCoerceSqlExprValueList (EList v)  = v
+veryUnsafeCoerceSqlExprValueList EEmptyList =
+  error "veryUnsafeCoerceSqlExprValueList: empty list."
 
 
 ----------------------------------------------------------------------
diff --git a/test/Test.hs b/test/Test.hs
index dfcb849..0bddffc 100644
--- a/test/Test.hs
+++ b/test/Test.hs
@@ -271,6 +271,16 @@ main = do
                  return p
           liftIO $ ret `shouldBe` [ p2e ]
 
+      it "works with not_ . isNothing" $
+        run $ do
+          p1e <- insert' p1
+          _   <- insert' p2
+          ret <- select $
+                 from $ \p -> do
+                 where_ $ not_ (isNothing (p ^. PersonAge))
+                 return p
+          liftIO $ ret `shouldBe` [ p1e ]
+
       it "works for a many-to-many implicit join" $
         run $ do
           p1e@(Entity p1k _) <- insert' p1
@@ -476,6 +486,17 @@ main = do
           liftIO $ ret `shouldBe` [ Entity p1k p1
                                   , Entity p2k p2 ]
 
+      it "IN works for valList (null list)" $
+        run $ do
+          p1k <- insert p1
+          p2k <- insert p2
+          p3k <- insert p3
+          ret <- select $
+                 from $ \p -> do
+                 where_ (p ^. PersonName `in_` valList [])
+                 return p
+          liftIO $ ret `shouldBe` []
+
       it "IN works for subList_select" $
         run $ do
           p1k <- insert p1