Merge remote-tracking branch 'aherrmann/pr_coalesce_subquery'

src/Database/Esqueleto/Internal/Sql.hs

@@ -404,8 +404,8 @@ instance Esqueleto SqlQuery SqlExpr SqlBackend where
   avg_     = unsafeSqlFunction "AVG"
   lower_   = unsafeSqlFunction "LOWER"
 
-  coalesce              = unsafeSqlFunction "COALESCE"
-  coalesceDefault exprs = unsafeSqlFunction "COALESCE" . (exprs ++) . return . just
+  coalesce              = unsafeSqlFunctionParens "COALESCE"
+  coalesceDefault exprs = unsafeSqlFunctionParens "COALESCE" . (exprs ++) . return . just
 
   like    = unsafeSqlBinOp    " LIKE "
   (%)     = unsafeSqlValue    "'%'"
@@ -584,6 +584,16 @@ unsafeSqlExtractSubField subField arg =
           uncommas' $ map (\(ERaw _ f) -> f info) $ toArgList arg
     in ("EXTRACT" <> parens (subField <> " FROM " <> argsTLB), argsVals)
 
+-- | (Internal) A raw SQL function. Preserves parentheses around arguments.
+-- See 'unsafeSqlBinOp' for warnings.
+unsafeSqlFunctionParens :: UnsafeSqlFunctionArgument a =>
+                           TLB.Builder -> a -> SqlExpr (Value b)
+unsafeSqlFunctionParens name arg =
+  ERaw Never $ \info ->
+    let (argsTLB, argsVals) =
+          uncommas' $ map (\(ERaw p f) -> first (parensM p) (f info)) $ toArgList arg
+    in (name <> parens argsTLB, argsVals)
+
 
 class UnsafeSqlFunctionArgument a where
   toArgList :: a -> [SqlExpr (Value ())]

test/Test.hs

@@ -798,6 +798,28 @@ main = do
                                    , Value 5
                                    ]
 
+      it "works with sub-queries" $
+        run $ do
+          p1id <- insert p1
+          p2id <- insert p2
+          p3id <- insert p3
+          _    <- insert p4
+          _    <- insert p5
+          _ <- insert $ BlogPost "a" p1id
+          _ <- insert $ BlogPost "b" p2id
+          _ <- insert $ BlogPost "c" p3id
+          ret <- select $
+                 from $ \b -> do
+                   let sub =
+                           from $ \p -> do
+                           where_ (p ^. PersonId ==. b ^. BlogPostAuthorId)
+                           return $ p ^. PersonAge
+                   return $ coalesceDefault [sub_select sub] (val (42 :: Int))
+          liftIO $ ret `shouldBe` [ Value (36 :: Int)
+                                  , Value 42
+                                  , Value 17
+                                  ]
+
 #if defined(WITH_POSTGRESQL) || defined(WITH_MYSQL)
       it "works on PostgreSQL and MySQL with <2 arguments" $
         run $ do