Tick off fetch implementation

README.md

@@ -69,7 +69,8 @@ getScoreByAge conn = do
 - [x] Test negative integer decoding, especially for `Integer`
 - [ ] Implement time intervals
 - [ ] and zoned time decoding
-- [ ] Implement `fetch` (`fetch_` but with parameter passing)
+- [ ] How about `timezone`? This could prove problematic when the server and application have different time zones
+- [x] Implement `fetch` (`fetch_` but with parameter passing)
 - [ ] Implement JSON decoding
 - [ ] Implement (anonymous) composite types
 - [ ] Catch [UnicodeException](https://hackage.haskell.org/package/text-2.1/docs/Data-Text-Encoding-Error.html#t:UnicodeException) when decoding text

lib/Database/PostgreSQL/Opium.hs

@@ -16,6 +16,7 @@ module Database.PostgreSQL.Opium
   , FromField (..)
   , FromRow (..)
   , RawField (..)
+  , fetch
   , fetch_
   , toListColumnTable
   )
@@ -45,11 +46,17 @@ import qualified Database.PostgreSQL.LibPQ as LibPQ
 
 import Database.PostgreSQL.Opium.Error (Error (..), ErrorPosition (..))
 import Database.PostgreSQL.Opium.FromField (FromField (..), fromField, RawField (..))
+import Database.PostgreSQL.Opium.ToParamList (ToParamList (..))
 
-execParams :: Connection -> Text -> ExceptT Error IO Result
+execParams
-execParams conn query = do
+  :: ToParamList a
+  => Connection
+  -> Text
+  -> a
+  -> ExceptT Error IO Result
+execParams conn query params = do
   let queryBytes = Encoding.encodeUtf8 query
-  liftIO (LibPQ.execParams conn queryBytes [] LibPQ.Binary) >>= \case
+  liftIO (LibPQ.execParams conn queryBytes (toParamList params) LibPQ.Binary) >>= \case
     Nothing ->
       except $ Left ErrorNoResult
     Just result -> do
@@ -60,13 +67,21 @@ execParams conn query = do
         Nothing -> pure result
         Just message -> except $ Left $ ErrorInvalidResult status $ Encoding.decodeUtf8 message
 
-fetch_ :: forall a. FromRow a => Connection -> Text -> IO (Either Error [a])
+fetch
-fetch_ conn query = runExceptT $ do
+  :: forall a b. (ToParamList a, FromRow b)
-  result <- execParams conn query
+  => Connection
-  columnTable <- ExceptT $ getColumnTable @a Proxy result
+  -> Text
+  -> a
+  -> IO (Either Error [b])
+fetch conn query params = runExceptT $ do
+  result <- execParams conn query params
+  columnTable <- ExceptT $ getColumnTable @b Proxy result
   nRows <- liftIO $ LibPQ.ntuples result
   mapM (ExceptT . fromRow result columnTable) [0..nRows - 1]
 
+fetch_ :: forall a. FromRow a => Connection -> Text -> IO (Either Error [a])
+fetch_ conn query = fetch conn query ()
+
 newtype ColumnTable = ColumnTable (Vector (Column, Oid))
   deriving (Eq, Show)
 

lib/Database/PostgreSQL/Opium/FromField.hs

@@ -41,6 +41,9 @@ import qualified Database.PostgreSQL.Opium.Oid as Oid
 (\/) :: (a -> Bool) -> (a -> Bool) -> a -> Bool
 p \/ q = \x -> p x || q x
 
+eq :: Eq a => a -> a -> Bool
+eq = (==)
+
 fromField :: FromField a => ByteString -> Either String a
 fromField =
   AP.parseOnly parseField
@@ -52,13 +55,13 @@ class FromField a where
 -- | See https://www.postgresql.org/docs/current/datatype-binary.html.
 -- Accepts @bytea@.
 instance FromField ByteString where
-  validOid Proxy = Oid.bytea
+  validOid Proxy = eq Oid.bytea
   parseField = AP.takeByteString
 
 -- | See https://www.postgresql.org/docs/current/datatype-character.html.
 -- Accepts @text@, @character@ and @character varying@.
 instance FromField Text where
-  validOid Proxy = Oid.text \/ Oid.character \/ Oid.characterVarying
+  validOid Proxy = eq Oid.text \/ eq Oid.character \/ eq Oid.characterVarying
   parseField = Encoding.decodeUtf8 <$> AP.takeByteString
 
 -- Accepts @text@, @character@ and @character varying@.
@@ -98,22 +101,22 @@ readWord bs = case BS.length bs of
 -- | See https://www.postgresql.org/docs/current/datatype-numeric.html.
 -- We assume that 'Int' has 64 bits. This is not guaranteed but reasonable enough.
 instance FromField Int where
-  validOid Proxy = Oid.smallint \/ Oid.integer \/ Oid.bigint
+  validOid Proxy = eq Oid.smallint \/ eq Oid.integer \/ eq Oid.bigint
   parseField = readInt =<< AP.takeByteString
 
 -- | See https://www.postgresql.org/docs/current/datatype-numeric.html.
 instance FromField Integer where
-  validOid Proxy = Oid.smallint \/ Oid.integer \/ Oid.bigint
+  validOid Proxy = eq Oid.smallint \/ eq Oid.integer \/ eq Oid.bigint
   parseField = readInt =<< AP.takeByteString
 
 instance FromField Word where
-  validOid Proxy = Oid.smallint \/ Oid.integer \/ Oid.bigint
+  validOid Proxy = eq Oid.smallint \/ eq Oid.integer \/ eq Oid.bigint
   parseField = readWord =<< AP.takeByteString
 
 -- | See https://www.postgresql.org/docs/current/datatype-numeric.html.
 -- Accepts only @real@ fields, not @double precision@.
 instance FromField Float where
-  validOid Proxy = Oid.real
+  validOid Proxy = eq Oid.real
   -- Afaict there's no cleaner (@base@) way to access the underlying bits.
   -- In C we'd do
   --
@@ -125,7 +128,7 @@ instance FromField Float where
 -- | See https://www.postgresql.org/docs/current/datatype-numeric.html.
 -- Accepts only @double precision@ fields, not @real@.
 instance FromField Double where
-  validOid Proxy = Oid.doublePrecision
+  validOid Proxy = eq Oid.doublePrecision
   parseField = unsafeCoerce <$> readBigEndian @Word <$> AP.takeByteString
 
 boolParser :: Parser Bool
@@ -136,7 +139,7 @@ boolParser = AP.choice
 
 -- | See https://www.postgresql.org/docs/current/datatype-boolean.html.
 instance FromField Bool where
-  validOid Proxy = Oid.boolean
+  validOid Proxy = eq Oid.boolean
   parseField = boolParser
 
 postgresEpoch :: Day
@@ -151,14 +154,14 @@ fromPostgresJulian x = addDays x postgresEpoch
 -- In short, Postgres treats 1 BC as a leap year and doesn't have a year zero.
 -- This means that working with negative dates will be different in Postgres and your application code.
 instance FromField Day where
-  validOid Proxy = Oid.date
+  validOid Proxy = eq Oid.date
   parseField = fromPostgresJulian . fromIntegral <$> readBigEndian @Int32 <$> AP.takeByteString
 
 -- | See https://www.postgresql.org/docs/current/datatype-datetime.html.
 -- Binary format: https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/utils/adt/date.c;h=ae0f24de2c3c54eb6d0405cdb212597c2407238e;hb=HEAD#l1542.
 -- Accepts @time@.
 instance FromField DiffTime where
-  validOid Proxy = Oid.time
+  validOid Proxy = eq Oid.time
   parseField = microsecondsToDiffTime . fromIntegral <$> readBigEndian @Int <$> AP.takeByteString
     where
       microsecondsToDiffTime :: Integer -> DiffTime
@@ -168,7 +171,7 @@ instance FromField DiffTime where
 -- Binary format: https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/utils/adt/date.c;h=ae0f24de2c3c54eb6d0405cdb212597c2407238e;hb=HEAD#l1542.
 -- Accepts @time@.
 instance FromField TimeOfDay where
-  validOid Proxy = Oid.time
+  validOid Proxy = eq Oid.time
   parseField = timeToTimeOfDay <$> parseField @DiffTime
 
 fromPostgresTimestamp :: Int -> (Day, DiffTime)
@@ -181,7 +184,7 @@ fromPostgresTimestamp ts = (day, time)
 -- | See https://www.postgresql.org/docs/current/datatype-datetime.html.
 -- Accepts @timestamp with timezone@.
 instance FromField UTCTime where
-  validOid Proxy = Oid.timestampWithTimezone
+  validOid Proxy = eq Oid.timestampWithTimezone
   parseField = toUTCTime . fromPostgresTimestamp <$> readBigEndian @Int <$> AP.takeByteString
     where
       toUTCTime (day, time) = UTCTime day time

lib/Database/PostgreSQL/Opium/Oid.hs

@@ -2,65 +2,62 @@ module Database.PostgreSQL.Opium.Oid where
 
 import Database.PostgreSQL.LibPQ (Oid (..))
 
-eq :: Eq a => a -> a -> Bool
-eq = (==)
-
 -- raw byte string
 
-bytea :: Oid -> Bool
+bytea :: Oid
-bytea = eq $ Oid 17
+bytea = Oid 17
 
 -- string types
 
-text :: Oid -> Bool
+text :: Oid
-text = eq $ Oid 25
+text = Oid 25
 
-character :: Oid -> Bool
+character :: Oid
-character = eq $ Oid 1042
+character = Oid 1042
 
-characterVarying :: Oid -> Bool
+characterVarying :: Oid
-characterVarying = eq $ Oid 1043
+characterVarying = Oid 1043
 
 -- integer types
 
 -- | 16-bit integer
-smallint :: Oid -> Bool
+smallint :: Oid
-smallint = eq $ Oid 21
+smallint = Oid 21
 
 -- | 32-bit integer
-integer :: Oid -> Bool
+integer :: Oid
-integer = eq $ Oid 23
+integer = Oid 23
 
 -- | 64-bit integer
-bigint :: Oid -> Bool
+bigint :: Oid
-bigint = eq $ Oid 20
+bigint = Oid 20
 
 -- floating point types
 
 -- | 32-bit IEEE float
-real :: Oid -> Bool
+real :: Oid
-real = eq $ Oid 700
+real = Oid 700
 
 -- | 64-bit IEEE float
-doublePrecision :: Oid -> Bool
+doublePrecision :: Oid
-doublePrecision = eq $ Oid 701
+doublePrecision = Oid 701
 
--- | Boolean
+-- | Oid
-boolean :: Oid -> Bool
+boolean :: Oid
-boolean = eq $ Oid 16
+boolean = Oid 16
 
 -- | Single days/dates.
-date :: Oid -> Bool
+date :: Oid
-date = eq $ Oid 1082
+date = Oid 1082
 
 -- | Time of day.
-time :: Oid -> Bool
+time :: Oid
-time = eq $ Oid 1083
+time = Oid 1083
 
 -- | A point in time.
-timestamp :: Oid -> Bool
+timestamp :: Oid
-timestamp = eq $ Oid 1114
+timestamp = Oid 1114
 
 -- | A point in time.
-timestampWithTimezone :: Oid -> Bool
+timestampWithTimezone :: Oid
-timestampWithTimezone = eq $ Oid 1184
+timestampWithTimezone = Oid 1184

lib/Database/PostgreSQL/Opium/ToField.hs

@@ -0,0 +1,50 @@
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE TypeApplications #-}
+
+module Database.PostgreSQL.Opium.ToField
+  ( ToField (..)
+  ) where
+
+import Data.Bits (Bits (..))
+import Data.ByteString (ByteString)
+import Data.List (singleton)
+import Data.Text (Text)
+import Data.Word (Word32)
+import Database.PostgreSQL.LibPQ (Format (..), Oid)
+import Unsafe.Coerce (unsafeCoerce)
+
+import qualified Data.ByteString as BS
+import qualified Data.Text as Text
+import qualified Data.Text.Encoding as Encoding
+import qualified Database.PostgreSQL.Opium.Oid as Oid
+
+class ToField a where
+  toField :: a -> Maybe (Oid, ByteString, Format)
+
+instance ToField ByteString where
+  toField x = Just (Oid.bytea, x, Binary)
+
+instance ToField Text where
+  toField x = Just (Oid.text, Encoding.encodeUtf8 x, Binary)
+
+instance ToField String where
+  toField = toField . Text.pack
+
+instance ToField Char where
+  toField = toField . singleton
+
+-- Potentially slow, but good enough for now
+encodeBigEndian :: (Integral a, Bits a) => Int -> a -> ByteString
+encodeBigEndian n = BS.pack . go [] n
+  where
+    go acc 0 _ = acc
+    go acc i x = go (fromIntegral (x .&. 0xff) : acc) (i - 1) (x `shiftR` 8)
+
+instance ToField Int where
+  toField x = Just (Oid.bigint, encodeBigEndian 8 x, Binary)
+
+instance ToField Float where
+  toField x = Just (Oid.real, encodeBigEndian @Word32 4 $ unsafeCoerce x, Binary)
+
+instance ToField Double where
+  toField x = Just (Oid.doublePrecision, encodeBigEndian @Word 8 $ unsafeCoerce x, Binary)

lib/Database/PostgreSQL/Opium/ToParamList.hs

@@ -0,0 +1,62 @@
+{-# LANGUAGE DefaultSignatures #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE TypeOperators #-}
+
+module Database.PostgreSQL.Opium.ToParamList
+  ( ToParamList (..)
+  ) where
+
+import Data.ByteString (ByteString)
+import Data.Functor.Identity (Identity)
+import Database.PostgreSQL.LibPQ (Format, Oid)
+import GHC.Generics (Generic, K1 (..), M1 (..), Rec0, Rep, U1 (..), from, (:*:) (..))
+
+import Database.PostgreSQL.Opium.ToField (ToField (..))
+
+class ToParamList a where
+  toParamList :: a -> [Maybe (Oid, ByteString, Format)]
+  default toParamList :: (Generic a, ToParamList' (Rep a)) => a -> [Maybe (Oid, ByteString, Format)]
+  toParamList = toParamList' . from
+
+instance ToField a => ToParamList [a] where
+  toParamList = map toField
+
+instance ToParamList () where
+
+instance ToField a => ToParamList (Identity a) where
+
+instance (ToField a, ToField b) => ToParamList (a, b) where
+
+instance (ToField a, ToField b, ToField c) => ToParamList (a, b, c) where
+
+instance (ToField a, ToField b, ToField c, ToField d) => ToParamList (a, b, c, d) where
+
+instance (ToField a, ToField b, ToField c, ToField d, ToField e) => ToParamList (a, b, c, d, e) where
+
+instance (ToField a, ToField b, ToField c, ToField d, ToField e, ToField f) => ToParamList (a, b, c, d, e, f) where
+
+instance (ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g) => ToParamList (a, b, c, d, e, f, g) where
+
+instance (ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g, ToField h) => ToParamList (a, b, c, d, e, f, g, h) where
+
+instance (ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g, ToField h, ToField i) => ToParamList (a, b, c, d, e, f, g, h, i) where
+
+instance (ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g, ToField h, ToField i, ToField j) => ToParamList (a, b, c, d, e, f, g, h, i, j) where
+
+instance (ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g, ToField h, ToField i, ToField j, ToField k) => ToParamList (a, b, c, d, e, f, g, h, i, j, k) where
+
+class ToParamList' f where
+  toParamList' :: f p -> [Maybe (Oid, ByteString, Format)]
+
+instance ToField t => ToParamList' (Rec0 t) where
+  toParamList' (K1 x) = [toField x]
+
+instance ToParamList' f => ToParamList' (M1 t c f) where
+  toParamList' (M1 x) = toParamList' x
+
+instance ToParamList' U1 where
+  toParamList' U1 = []
+
+instance (ToParamList' f, ToParamList' g) => ToParamList' (f :*: g) where
+  toParamList' (x :*: y) = toParamList' x ++ toParamList' y

test/Database/PostgreSQL/OpiumSpec.hs

@@ -7,6 +7,7 @@
 module Database.PostgreSQL.OpiumSpec (spec) where
 
 import Data.ByteString (ByteString)
+import Data.Functor.Identity (Identity (..))
 import Data.Proxy (Proxy (..))
 import Data.Text (Text)
 import Database.PostgreSQL.LibPQ (Connection)
@@ -46,6 +47,12 @@ data ScoreByAge = ScoreByAge
 
 instance Opium.FromRow ScoreByAge where
 
+data Only a = Only
+  { only :: a
+  } deriving (Eq, Generic, Show)
+
+instance Opium.FromField a => Opium.FromRow (Only a) where
+
 isLeft :: Either a b -> Bool
 isLeft (Left _) = True
 isLeft _ = False
@@ -117,6 +124,15 @@ spec = do
       row <- Opium.fromRow result columnTable 0
       row `shouldBe` Right (ManyFields "abc" 42 1.0 "test" True)
 
+  describe "fetch" $ do
+    it "Passes numbered parameters and retrieves a list of rows" $ \conn -> do
+      rows <- Opium.fetch conn "SELECT ($1 + $2) AS only" (17 :: Int, 25 :: Int)
+      rows `shouldBe` Right [Only (42 :: Int)]
+
+    it "Uses Identity to pass single parameters" $ \conn -> do
+      rows <- Opium.fetch conn "SELECT count(*) AS only FROM person WHERE name = $1" $ Identity ("paul" :: Text)
+      rows `shouldBe` Right [Only (1 :: Int)]
+
   describe "fetch_" $ do
     it "Retrieves a list of rows" $ \conn -> do
       rows <- Opium.fetch_ conn "SELECT * FROM person"