Fix a marshalling error for columns of type Maybe (Vector a)

beam-postgres/ChangeLog.md

@@ -1,3 +1,9 @@
+# Unreleased
+
+## Bug fixes
+
+ * Fixed an issue where columns of type `Maybe (Vector a)` did not marshall correctly from the database. In particular, querying a `Nothing` would return `Just (Vector.fromList [])` instead (#692).
+
 # 0.5.4.1
 
 ## Bug fixes

beam-postgres/Database/Beam/Postgres/Types.hs

@@ -155,12 +155,7 @@ instance FromBackendRow Postgres [Char]
 instance FromBackendRow Postgres (Ratio Integer)
 instance FromBackendRow Postgres (CI Text)
 instance FromBackendRow Postgres (CI TL.Text)
-instance (Pg.FromField a, Typeable a) => FromBackendRow Postgres (Vector a) where
-  fromBackendRow = do
-      isNull <- peekField
-      case isNull of
-        Just SqlNull -> pure mempty
-        Nothing -> parseOneField @Postgres @(Vector a)
+instance (Pg.FromField a, Typeable a) => FromBackendRow Postgres (Vector a)
 instance (Pg.FromField a, Typeable a) => FromBackendRow Postgres (Pg.PGArray a)
 instance FromBackendRow Postgres (Pg.Binary ByteString)
 instance FromBackendRow Postgres (Pg.Binary BL.ByteString)

beam-postgres/test/Database/Beam/Postgres/Test/Marshal.hs

@@ -1,4 +1,5 @@
 {-# LANGUAGE AllowAmbiguousTypes #-}
+{-# LANGUAGE StandaloneDeriving #-}
 module Database.Beam.Postgres.Test.Marshal where
 
 import           Database.Beam
@@ -9,6 +10,7 @@ import           Database.Beam.Migrate.Simple (autoMigrate)
 import           Database.Beam.Postgres
 import           Database.Beam.Postgres.Migrate (migrationBackend)
 import           Database.Beam.Postgres.Test
+import           Database.PostgreSQL.Simple (execute_)
 
 import           Data.ByteString (ByteString)
 import           Data.Functor.Classes
@@ -17,6 +19,7 @@ import qualified Data.Text as T
 import           Data.Typeable
 import           Data.UUID (UUID, fromWords)
 import           Data.Word
+import qualified Data.Vector as Vector
 
 import qualified Hedgehog
 import           Hedgehog ((===))
@@ -28,6 +31,7 @@ import           Test.Tasty.HUnit
 
 import           Unsafe.Coerce
 
+
 textGen :: Hedgehog.Gen T.Text
 textGen = Gen.text (Range.constant 0 1000) $ Gen.filter (/= '\NUL') Gen.unicode
 
@@ -86,6 +90,7 @@ tests postgresConn =
     , marshalTest (Gen.maybe (Gen.integral (Range.constantBounded @Word64))) postgresConn
     , marshalTest (Gen.maybe textGen) postgresConn
     , marshalTest (Gen.maybe uuidGen) postgresConn
+    , marshalTest692 postgresConn
 
     , marshalTest' (\a b -> Hedgehog.assert (liftEq ptCmp a b))  (Gen.maybe pointGen) postgresConn
     , marshalTest' (\a b -> Hedgehog.assert (liftEq boxCmp a b)) (Gen.maybe boxGen) postgresConn
@@ -160,3 +165,69 @@ marshalTest' cmp gen postgresConn =
 
     assertBool "Hedgehog test failed" passes
 
+
+-- Ensure that both `Vector Text` and `Maybe (Vector Text)` can be 
+-- marshalled correctly (see issue 692).
+--
+-- At this time, the postgres migration backend can't create columns of arrays,
+-- and hence this test does not use `marshalTest`.
+marshalTest692 :: IO ByteString -> TestTree
+marshalTest692 postgresConn = 
+  testCase "Can marshal Vector Text and Maybe (Vector Text) (#692)" $ 
+  withTestPostgres ("db_marshal_maybe_vector_text_issue_692") postgresConn $ \conn -> do
+    liftIO $ execute_ conn $ "CREATE TABLE mytable (\nmyid SERIAL PRIMARY KEY, mycolumn text[], mynullablecolumn text[]\n);"
+
+    passes <- Hedgehog.check . Hedgehog.property $ do
+      nullable <- Hedgehog.forAll (Gen.maybe (Vector.fromList <$> (Gen.list (Range.linear 0 10) textGen)))
+      nonnull <- Hedgehog.forAll (Vector.fromList <$> (Gen.list (Range.linear 0 10) textGen))
+
+      [MkTbl692 rowId v vnull] <-
+        liftIO . runBeamPostgres conn 
+          $ runInsertReturningList 
+            $ insert (_myTable myDB) 
+              $ insertExpressions [ MkTbl692 default_ (val_ nonnull) (val_ nullable) ]
+
+      v === nonnull
+      vnull === nullable
+
+      Just (MkTbl692 _ v' vnull') <-
+          liftIO . runBeamPostgres conn 
+            $ runSelectReturningOne (lookup_ (_myTable myDB) (Tbl692Key rowId))
+      v' === nonnull
+      vnull' === nullable
+
+    assertBool "Hedgehog test failed" passes
+  where
+    myDB :: DatabaseSettings Postgres MyDB692
+    myDB = defaultDbSettings `withDbModification`
+            MkMyDB692 {
+              _myTable =
+                setEntityName "mytable" <>
+                modifyTableFields
+                  tableModification {
+                    myid = fieldNamed "myid",
+                    mycolumn = fieldNamed "mycolumn",
+                    mynullablecolumn = fieldNamed "mynullablecolumn"
+                  }
+            }
+
+data Tbl692 f
+    = MkTbl692 
+    { myid             :: C f (SqlSerial Int32)
+    , mycolumn         :: C f (Vector.Vector T.Text)
+    , mynullablecolumn :: C f (Maybe (Vector.Vector T.Text)) 
+    }
+      deriving (Generic, Beamable)
+
+deriving instance Show (Tbl692 Identity)
+deriving instance Eq (Tbl692 Identity)
+
+instance Table Tbl692 where
+    data PrimaryKey Tbl692 f = Tbl692Key (C f (SqlSerial Int32))
+      deriving (Generic, Beamable)
+    primaryKey = Tbl692Key <$> myid
+data MyDB692 entity
+    = MkMyDB692
+    { _myTable :: entity (TableEntity Tbl692)
+    } deriving (Generic)
+instance Database Postgres MyDB692