feat: optional

src/Data.Postgres.Extract.Record.purs

@@ -5,8 +5,9 @@ import Prelude
 import Control.Monad.Error.Class (liftMaybe)
 import Data.Array as Array
 import Data.Either (Either)
-import Data.Maybe (fromMaybe)
+import Data.Maybe (Maybe, fromMaybe, isJust)
 import Data.Postgres.Types (RawRow(..))
+import Data.Traversable (sequence, traverse)
 import Database.PostgreSQL (class FromSQLValue, fromSQLValue)
 import Foreign (Foreign)
 import Prim.Row (class Cons, class Lacks)
@@ -16,6 +17,15 @@ import Type.Prelude (class IsSymbol, Proxy(..))
 
 data ExtractRecord a = ExtractRecord (Array Foreign) a
 
+instance Functor ExtractRecord where
+  map f (ExtractRecord rs a) = ExtractRecord rs (f a)
+
+instance Apply ExtractRecord where
+  apply (ExtractRecord _ f) (ExtractRecord rs a) = ExtractRecord rs (f a)
+
+instance Applicative ExtractRecord where
+  pure a = ExtractRecord [] a
+
 extract :: forall a. (ExtractRecord {} -> Either String $ ExtractRecord a) -> RawRow -> Either String a
 extract f = map finish <<< f <<< start
 
@@ -43,3 +53,21 @@ field (ExtractRecord row r) = do
   col <- liftMaybe eempty $ Array.head row
   val <- fromSQLValue col
   pure $ skip $ ExtractRecord row $ Record.insert (Proxy @k) val r
+
+optional
+  :: forall a b @k @v
+   . Show (Record a)
+  => Lacks k a
+  => Cons k v a b
+  => IsSymbol k
+  => FromSQLValue (Maybe v)
+  => ExtractRecord $ Record a
+  -> Either String $ ExtractRecord $ Maybe $ Record b
+optional (ExtractRecord row r) = do
+  let
+    col = Array.head row
+    skip' = if isJust col then skip else identity
+  val :: Maybe v <- map join $ traverse fromSQLValue col
+  pure
+    $ sequence
+    $ map (\v -> skip' $ ExtractRecord row $ Record.insert (Proxy @k) v r) val