Add FromField Char

lib/Database/PostgreSQL/Opium/FromField.hs

@@ -9,6 +9,7 @@ module Database.PostgreSQL.Opium.FromField
 
 import Data.Attoparsec.Text
   ( Parser
+  , anyChar
   , choice
   , decimal
   , double
@@ -38,14 +39,22 @@ class FromField a where
   validOid :: Proxy a -> Oid -> Bool
   parseField :: Parser a
 
+-- | See https://www.postgresql.org/docs/current/datatype-character.html.
 instance FromField Text where
   validOid _ = Oid.text \/ Oid.character \/ Oid.characterVarying
   parseField = takeText
 
+-- | See https://www.postgresql.org/docs/current/datatype-character.html.
 instance FromField String where
   validOid _ = validOid @Text Proxy
   parseField = Text.unpack <$> parseField
 
+-- | See https://www.postgresql.org/docs/current/datatype-character.html.
+-- This instance accepts all character types but fails to decode fields that are not exactly one character.
+instance FromField Char where
+  validOid _ = validOid @Text Proxy
+  parseField = anyChar
+
 instance FromField Int where
   validOid _ = Oid.smallint \/ Oid.integer \/ Oid.bigint
   parseField = signed decimal