Add stringAgg to PostgreSQL module (fixes #98).

src/Database/Esqueleto/PostgreSQL.hs

@@ -5,8 +5,11 @@
 -- /Since: 2.2.8/
 module Database.Esqueleto.PostgreSQL
   ( arrayAgg
+  , stringAgg
   ) where
 
+import Data.String (IsString)
+
 import Database.Esqueleto.Internal.Language
 import Database.Esqueleto.Internal.Sql
 
@@ -17,3 +20,15 @@ import Database.Esqueleto.Internal.Sql
 -- /Since: 2.2.8/
 arrayAgg :: SqlExpr (Value a) -> SqlExpr (Value [a])
 arrayAgg = unsafeSqlFunction "array_agg"
+
+
+-- | (@string_agg@) Concatenate input values separated by a
+-- delimiter.
+--
+-- /Since: 2.2.8/
+stringAgg
+  :: IsString s
+  => SqlExpr (Value s) -- ^ Input values.
+  -> SqlExpr (Value s) -- ^ Delimiter.
+  -> SqlExpr (Value s) -- ^ Concatenation.
+stringAgg expr delim = unsafeSqlFunction "string_agg" (expr, delim)

test/Test.hs

@@ -1330,6 +1330,16 @@ main = do
             from $ \p -> do
             return (EP.arrayAgg (p ^. PersonName))
           liftIO $ L.sort ret `shouldBe` L.sort (map personName people)
+
+      it "stringAgg looks sane" $
+        run $ do
+          let people = [p1, p2, p3, p4, p5]
+          mapM_ insert people
+          [Value ret] <-
+            select $
+            from $ \p -> do
+            return (EP.stringAgg (p ^. PersonName) (val " "))
+          liftIO $ L.sort (words ret) `shouldBe` L.sort (map personName people)
 #endif