Add support for datetimeoffset data type

src/Database/ODBC/Conversion.hs

@@ -116,6 +116,12 @@ instance FromValue LocalTime where
        LocalTimeValue x -> pure (id x)
        v -> Left ("Expected LocalTime, but got: " ++ show v))
 
+instance FromValue ZonedTime where
+  fromValue =
+    (\case
+       ZonedTimeValue lt tz -> pure (ZonedTime lt tz)
+       v -> Left ("Expected ZonedTime, but got: " ++ show v))
+
 --------------------------------------------------------------------------------
 -- Producing rows
 

src/Database/ODBC/SQLServer.hs

@@ -35,6 +35,7 @@ module Database.ODBC.SQLServer
   , Internal.Binary(..)
   , Datetime2(..)
   , Smalldatetime(..)
+  , Datetimeoffset(..)
 
     -- * Streaming results
     -- $streaming
@@ -257,6 +258,22 @@ newtype Smalldatetime = Smalldatetime
   { unSmalldatetime :: LocalTime
   } deriving (Eq, Ord, Show, Typeable, Generic, Data, FromValue)
 
+newtype Datetimeoffset = Datetimeoffset
+  { unDatetimeoffset :: ZonedTime
+  } deriving (Show, Typeable, Generic, Data, FromValue)
+
+-- SQL Server considers two datetimeoffset values to be equal as long as they
+-- represent the same instant in time; i.e. they are equavalent to the same UTC
+-- time and date. This instance reproduces that behaviour.
+instance Eq Datetimeoffset where
+  Datetimeoffset x == Datetimeoffset y = zonedTimeToUTC x == zonedTimeToUTC y
+
+-- SQL Server considers datetimeoffset values to be ordered according to their
+-- UTC equivalent values. This instance reproduces that behaviour.
+instance Ord Datetimeoffset where
+  compare (Datetimeoffset x) (Datetimeoffset y) =
+    compare (zonedTimeToUTC x) (zonedTimeToUTC y)
+
 --------------------------------------------------------------------------------
 -- Conversion to SQL
 
@@ -376,6 +393,9 @@ instance ToSql Smalldatetime where
       shrink (LocalTime dd (TimeOfDay hh mm _ss)) =
         LocalTime dd (TimeOfDay hh mm 0)
 
+instance ToSql Datetimeoffset where
+  toSql (Datetimeoffset (ZonedTime lt tzone)) = toSql $ ZonedTimeValue lt tzone
+
 --------------------------------------------------------------------------------
 -- Top-level functions
 
@@ -512,7 +532,12 @@ renderFractional x = trim (printf "%.7f" (realToFrac x :: Double) :: String)
                  s' -> s')
 
 renderTimeZone :: TimeZone -> String
-renderTimeZone tzone = if tzone == utc then "Z" else timeZoneOffsetString tzone
+renderTimeZone (TimeZone 0 _ _) = "Z"
+renderTimeZone (TimeZone t _ _) | t < 0 = '-' : renderTimeZone' (negate t)
+renderTimeZone (TimeZone t _ _) = '+' : renderTimeZone' t
+
+renderTimeZone' :: Int -> String
+renderTimeZone' t = printf "%02d:%02d" (t `div` 60) (t `mod` 60)
 
 -- | A very conservative character escape.
 escapeChar8 :: Word8 -> Text

test/Main.hs

@@ -39,7 +39,7 @@ import           Data.Word
 import           Database.ODBC.Conversion (FromValue(..))
 import           Database.ODBC.Internal (Value (..), Connection, ODBCException(..), Step(..), Binary)
 import qualified Database.ODBC.Internal as Internal
-import           Database.ODBC.SQLServer (Datetime2(..), Smalldatetime(..), ToSql(..))
+import           Database.ODBC.SQLServer (Datetime2(..), Smalldatetime(..), Datetimeoffset(..), ToSql(..))
 import qualified Database.ODBC.SQLServer as SQLServer
 import           Database.ODBC.TH (partsParser, Part(..))
 import           System.Environment
@@ -146,6 +146,7 @@ conversionTo = do
   quickCheckRoundtrip @Datetime2 "Datetime2" "datetime2"
   quickCheckRoundtrip @Smalldatetime "Smalldatetime" "smalldatetime"
   quickCheckRoundtrip @TestDateTime "TestDateTime" "datetime"
+  quickCheckRoundtrip @Datetimeoffset "Datetimeoffset" "datetimeoffset"
   quickCheckOneway @TimeOfDay "TimeOfDay" "time"
   quickCheckRoundtrip @TestTimeOfDay "TimeOfDay" "time"
   quickCheckRoundtrip @Float "Float" "real"
@@ -678,3 +679,9 @@ instance Arbitrary Smalldatetime where
     pure
       (Smalldatetime
          (LocalTime day (timeToTimeOfDay (secondsToDiffTime (minutes * 60)))))
+
+instance Arbitrary Datetimeoffset where
+  arbitrary = do
+    lt <- arbitrary
+    offset <- choose (-12 * 60, 14 * 60)
+    return $ Datetimeoffset $ ZonedTime lt $ TimeZone offset False ""