Add ToField Day

lib/Database/PostgreSQL/Opium/ToField.hs

@@ -7,8 +7,10 @@ module Database.PostgreSQL.Opium.ToField
 
 import Data.Bits (Bits (..))
 import Data.ByteString (ByteString)
+import Data.Int (Int32)
 import Data.List (singleton)
 import Data.Text (Text)
+import Data.Time (Day, diffDays, fromGregorian)
 import Data.Word (Word32)
 import Database.PostgreSQL.LibPQ (Format (..), Oid)
 import Unsafe.Coerce (unsafeCoerce)
@@ -48,3 +50,11 @@ instance ToField Float where
 
 instance ToField Double where
   toField x = Just (Oid.doublePrecision, encodeBigEndian @Word 8 $ unsafeCoerce x, Binary)
+
+toPostgresJulian :: Day -> Integer
+toPostgresJulian date = diffDays date postgresEpoch
+  where
+    postgresEpoch = fromGregorian 2000 1 1
+
+instance ToField Day where
+  toField x = Just (Oid.date, encodeBigEndian @Int32 4 $ fromIntegral $ toPostgresJulian x, Binary)