Set system to aarch64-darwin

README.md

@@ -34,7 +34,7 @@ data User = User
 instance Opium.FromRow User where
 
 getUsers :: Connection -> IO (Either Opium.Error [User])
-getUsers conn = Opium.fetch_ "SELECT * FROM user" conn
+getUsers = Opium.fetch_ "SELECT * FROM user"
 ```
 
 The `Opium.FromRow` instance is implemented generically for all product types ("records"). It looks up the field name in the query result and decodes the column value using `Opium.FromField`.
@@ -51,7 +51,7 @@ instance Opium.FromRow ScoreByAge where
 getScoreByAge :: Connection -> IO ScoreByAge
 getScoreByAge conn = do
   let query = "SELECT regr_intercept(score, age) AS t, regr_slope(score, age) AS m FROM user"
-  Right [x] <- Opium.fetch_ query conn
+  Right (Identity x) <- Opium.fetch_ query conn
   pure x
 ```
 

flake.nix

@@ -3,7 +3,7 @@
 
   outputs = { self, nixpkgs }:
     let
-      system = "x86_64-linux";
+      system = "aarch64-darwin";
       pkgs = nixpkgs.legacyPackages.${system};
       opium = pkgs.haskellPackages.developPackage {
         root = ./.;

lib/Database/PostgreSQL/Opium/FromRow.hs

@@ -53,12 +53,34 @@ class FromRow a where
   fromRow result columnTable row =
     runExceptT $ to <$> fromRow' @0 FRProxy (FromRowCtx result columnTable) row
 
+instance
+  ( Generic a
+  , GetColumnTable' (Rep a)
+  , FromRow' 0 (Rep a)
+  , Generic b
+  , GetColumnTable' (Rep b)
+  , FromRow' (NumberOfMembers (Rep a)) (Rep b)
+  ) => FromRow (a, b) where
+  getColumnTable Proxy result = runExceptT $ do
+    ctA <- newColumnTable <$> getColumnTable' @(Rep a) Proxy result
+    ctB <- newColumnTable <$> getColumnTable' @(Rep b) Proxy result
+    pure $ ctA `concatColumnTables` ctB
+
+  fromRow result ct row = runExceptT $ do
+    x <- to <$> fromRow' @0 FRProxy (FromRowCtx result ct) row
+    y <- to <$> fromRow' @(NumberOfMembers (Rep a)) FRProxy (FromRowCtx result ct) row
+    pure (x, y)
+
 newtype ColumnTable = ColumnTable (Vector (Column, Oid))
   deriving (Eq, Show)
 
 newColumnTable :: [(Column, Oid)] -> ColumnTable
 newColumnTable = ColumnTable . Vector.fromList
 
+concatColumnTables :: ColumnTable -> ColumnTable -> ColumnTable
+concatColumnTables (ColumnTable a) (ColumnTable b) =
+  ColumnTable $ a <> b
+
 indexColumnTable :: ColumnTable -> Int -> (Column, Oid)
 indexColumnTable (ColumnTable v) i = v `Vector.unsafeIndex` i
 

test/Database/PostgreSQL/OpiumSpec.hs

@@ -122,6 +122,13 @@ spec = do
       row <- Opium.fromRow result columnTable 0
       row `shouldBe` Right (ManyFields "abc" 42 1.0 "test" True)
 
+    it "Decodes multiple records into a tuple" $ \conn -> do
+      Just result <- LibPQ.execParams conn "SELECT 'albus' AS name, 123 AS age, 42 AS only" [] LibPQ.Binary
+      Right columnTable <- Opium.getColumnTable @(Person, Only Int) Proxy result
+
+      row <- Opium.fromRow @(Person, Only Int) result columnTable 0
+      row `shouldBe` Right (Person "albus" 123, Only 42)
+
   describe "fetch" $ do
     it "Passes numbered parameters and retrieves a list of rows" $ \conn -> do
       rows <- Opium.fetch "SELECT ($1 + $2) AS only" (17 :: Int, 25 :: Int) conn