Add array_agg function, new PostgreSQL module.

esqueleto.cabal

@@ -1,5 +1,5 @@
 name:                esqueleto
-version:             2.2.7
+version:             2.2.8
 synopsis:            Type-safe EDSL for SQL queries on persistent backends.
 homepage:            https://github.com/prowdsponsor/esqueleto
 license:             BSD3
@@ -57,6 +57,7 @@ Flag mysql
 library
   exposed-modules:
     Database.Esqueleto
+    Database.Esqueleto.PostgreSQL
     Database.Esqueleto.Internal.Language
     Database.Esqueleto.Internal.Sql
   other-modules:

src/Database/Esqueleto.hs

@@ -87,6 +87,9 @@ module Database.Esqueleto
   , (<#)
   , (<&>)
 
+    -- * RDBMS-specific modules
+    -- $rdbmsSpecificModules
+
     -- * Helpers
   , valkey
   , valJ
@@ -380,6 +383,22 @@ import qualified Database.Persist
 ----------------------------------------------------------------------
 
 
+-- $rdbmsSpecificModules
+--
+-- There are many differences between SQL syntax and functions
+-- supported by different RDBMSs.  Since version 2.2.8,
+-- @esqueleto@ includes modules containing functions that are
+-- specific to a given RDBMS.
+--
+--  * PostgreSQL: "Database.Esqueleto.PostgreSQL".
+--
+-- In order to use these functions, you need to explicitly import
+-- their corresponding modules, they're not re-exported here.
+
+
+----------------------------------------------------------------------
+
+
 -- | @valkey i = 'val' . 'toSqlKey'@
 -- (<https://github.com/prowdsponsor/esqueleto/issues/9>).
 valkey :: (Esqueleto query expr backend, ToBackendKey SqlBackend entity, PersistField (Key entity)) =>

src/Database/Esqueleto/PostgreSQL.hs

@@ -0,0 +1,19 @@
+{-# LANGUAGE OverloadedStrings
+ #-}
+-- | This module contain PostgreSQL-specific functions.
+--
+-- /Since: 2.2.8/
+module Database.Esqueleto.PostgreSQL
+  ( arrayAgg
+  ) where
+
+import Database.Esqueleto.Internal.Language
+import Database.Esqueleto.Internal.Sql
+
+
+-- | (@array_agg@) Concatenate input values, including @NULL@s,
+-- into an array.
+--
+-- /Since: 2.2.8/
+arrayAgg :: SqlExpr (Value a) -> SqlExpr (Value [a])
+arrayAgg = unsafeSqlFunction "array_agg"

test/Test.hs

@@ -53,6 +53,7 @@ import qualified Control.Monad.Trans.Resource as R
 import qualified Data.List as L
 import qualified Data.Set as S
 import qualified Data.Text.Lazy.Builder as TLB
+import qualified Database.Esqueleto.PostgreSQL as EP
 import qualified Database.Esqueleto.Internal.Sql as EI
 
 
@@ -1313,6 +1314,24 @@ main = do
       it "looks sane for ForShare"        $ sanityCheck ForShare        "FOR SHARE"
       it "looks sane for LockInShareMode" $ sanityCheck LockInShareMode "LOCK IN SHARE MODE"
 
+    describe "PostgreSQL module" $ do
+      it "should be tested on the PostgreSQL database" $
+#if !defined(WITH_POSTGRESQL)
+        pendingWith "test suite not running under PostgreSQL, skipping"
+#else
+        (return () :: IO ())
+
+      it "arrayAgg looks sane" $
+        run $ do
+          let people = [p1, p2, p3, p4, p5]
+          mapM_ insert people
+          [Value ret] <-
+            select $
+            from $ \p -> do
+            return (EP.arrayAgg (p ^. PersonName))
+          liftIO $ L.sort ret `shouldBe` L.sort (map personName people)
+#endif
+
 
 ----------------------------------------------------------------------