Fix distinctOnOrderBy with nested expression (#278)

* Fix stripped part of nested expression during
assembling of `distinctOnOrderBy` subexpression

* Bump version number and update changelog

changelog.md

@@ -1,3 +1,9 @@
+3.5.2.2
+=======
+- @NikitaRazmakhnin
+  - [#278](https://github.com/bitemyapp/esqueleto/pull/278)
+        - Fix generating of bad sql using nexted expressions with `distinctOnOrderBy`.
+
 3.5.2.1
 =======
 - @cdparks

esqueleto.cabal

@@ -1,7 +1,7 @@
 cabal-version: 1.12
 
 name:           esqueleto
-version:        3.5.2.1
+version:        3.5.2.2
 synopsis:       Type-safe EDSL for SQL queries on persistent backends.
 description:    @esqueleto@ is a bare bones, type-safe EDSL for SQL queries that works with unmodified @persistent@ SQL backends.  Its language closely resembles SQL, so you don't have to learn new concepts, just new syntax, and it's fairly easy to predict the generated SQL and optimize it for your backend. Most kinds of errors committed when writing SQL are caught as compile-time errors---although it is possible to write type-checked @esqueleto@ queries that fail at runtime.
                 .

src/Database/Esqueleto/Internal/Internal.hs

@@ -374,7 +374,11 @@ distinctOnOrderBy exprs act =
     toDistinctOn :: SqlExpr OrderBy -> SqlExpr DistinctOn
     toDistinctOn (ERaw m f) = ERaw m $ \p info ->
         let (b, vals) = f p info
-        in (TLB.fromLazyText $ head $ TL.splitOn " " $ TLB.toLazyText b, vals)
+        in  ( TLB.fromLazyText
+              $ TL.replace " DESC" ""
+              $ TL.replace " ASC" ""
+              $ TLB.toLazyText b
+            , vals )
 
 -- | @ORDER BY random()@ clause.
 --

test/PostgreSQL/Test.hs

@@ -220,6 +220,12 @@ testSelectDistinctOn = do
       slightlyLessSimpleTest $ \bp ->
         distinctOnOrderBy [asc (bp ^. BlogPostAuthorId), asc (bp ^. BlogPostTitle)]
 
+    itDb "generates correct sql with nested expression (distinctOnOrderBy)" $ do
+      let query = do
+            let orderVal = coalesce [nothing, just $ val (10 :: Int)]
+            distinctOnOrderBy [ asc orderVal, desc orderVal ] $ pure orderVal
+      select query
+      asserting noExceptions