Make getColumnTable report missing columns

lib/Database/PostgreSQL/Opium.hs

@@ -62,16 +62,16 @@ fetchResult result = do
   runExceptT $ mapM (ExceptT . flip fromRow result) [0..nRows - 1]
 
 class FromRow a where
-  getColumnTable :: Proxy a -> Result -> IO [LibPQ.Column]
-  default getColumnTable :: (Generic a, GetColumnTable' (Rep a)) => Proxy a -> Result -> IO [LibPQ.Column]
-  getColumnTable Proxy = getColumnTable' @(Rep a) Proxy
+  getColumnTable :: Proxy a -> Result -> IO (Either Error [Column])
+  default getColumnTable :: (Generic a, GetColumnTable' (Rep a)) => Proxy a -> Result -> IO (Either Error [Column])
+  getColumnTable Proxy = runExceptT . getColumnTable' @(Rep a) Proxy
 
   fromRow :: Row -> Result -> IO (Either Error a)
   default fromRow :: (Generic a, FromRow' (Rep a)) => Row -> Result -> IO (Either Error a)
   fromRow row result = fmap to <$> fromRow' row result
 
 class GetColumnTable' f where
-  getColumnTable' :: Proxy (f p) -> Result -> IO [LibPQ.Column]
+  getColumnTable' :: Proxy (f p) -> Result -> ExceptT Error IO [Column]
 
 instance GetColumnTable' f => GetColumnTable' (M1 D c f) where
   getColumnTable' Proxy = getColumnTable' @f Proxy
@@ -83,17 +83,15 @@ instance (GetColumnTable' f, GetColumnTable' g) => GetColumnTable' (f :*: g) whe
   getColumnTable' Proxy result =
     (++) <$> getColumnTable' @f Proxy result <*> getColumnTable' @g Proxy result
 
-checkColumn :: FromField f => Proxy f -> String -> Result -> IO [Column]
-checkColumn Proxy nameStr result = LibPQ.fnumber result name >>= \case
-    Just column -> do
+checkColumn :: FromField f => Proxy f -> String -> Result -> ExceptT Error IO [Column]
+checkColumn Proxy nameStr result = do
+    column <- ExceptT $ maybe (Left $ ErrorMissingColumn nameText) Right <$> LibPQ.fnumber result name
     -- TODO: Rewrite FromField to check whether oid works for decoding t
-      _oid <- LibPQ.ftype result column
+    _oid <- ExceptT $ Right <$> LibPQ.ftype result column
     pure [column]
-    Nothing -> do
-      -- TODO: Return ErrorMissingColumn
-      undefined
     where
-      name = Encoding.encodeUtf8 $ Text.pack nameStr
+      nameText = Text.pack nameStr
+      name = Encoding.encodeUtf8 nameText
 
 instance {-# OVERLAPPABLE #-} (FromField t, KnownSymbol nameSym) => GetColumnTable' (M1 S ('MetaSel ('Just nameSym) nu ns dl) (Rec0 t)) where
   getColumnTable' Proxy = checkColumn @t Proxy $ symbolVal @nameSym Proxy

lib/Database/PostgreSQL/Opium/FromField.hs

@@ -29,6 +29,7 @@ p \/ q = \x -> p x || q x
 
 data FieldError
   = FieldErrorUnexpectedNull
+  -- TODO: Move this to the normal Error
   | FieldErrorInvalidOid Oid
   | FieldErrorInvalidField Oid Text String
   deriving (Eq, Show)

test/Database/PostgreSQL/OpiumSpec.hs

@@ -36,19 +36,24 @@ spec = do
     it "Gets the column table for a result" $ \conn -> do
       Just result <- LibPQ.execParams conn "SELECT name, age FROM person" [] LibPQ.Text
       columnTable <- Opium.getColumnTable @Person Proxy result
-      columnTable `shouldBe` [0, 1]
+      columnTable `shouldBe` Right [0, 1]
 
     it "Gets the numbers right for funky configurations" $ \conn -> do
       Just result0 <- LibPQ.execParams conn "SELECT age, name FROM person" [] LibPQ.Text
       columnTable0 <- Opium.getColumnTable @Person Proxy result0
-      columnTable0 `shouldBe` [1, 0]
+      columnTable0 `shouldBe` Right [1, 0]
 
       Just result1 <- LibPQ.execParams conn "SELECT 0 a, 1 b, 2 c, age, 4 d, name FROM person" [] LibPQ.Text
       columnTable1 <- Opium.getColumnTable @Person Proxy result1
-      columnTable1 `shouldBe` [5, 3]
+      columnTable1 `shouldBe` Right [5, 3]
+
+    it "Fails for missing columns" $ \conn -> do
+      Just result <- LibPQ.execParams conn "SELECT 0 a FROM person" [] LibPQ.Text
+      columnTable <- Opium.getColumnTable @Person Proxy result
+      columnTable `shouldBe` Left (Opium.ErrorMissingColumn "name")
 
   describe "fromRow" $ do
-    it "decodes rows in a Result" $ \conn -> do
+    it "Decodes rows in a Result" $ \conn -> do
       Just result <- LibPQ.execParams conn "SELECT * FROM person" [] LibPQ.Text
 
       row0 <- Opium.fromRow @Person (LibPQ.Row 0) result
@@ -57,35 +62,31 @@ spec = do
       row1 <- Opium.fromRow @Person (LibPQ.Row 1) result
       row1 `shouldBe` Right (Person "albus" 103)
 
-    it "decodes NULL into Nothing for Maybes" $ \conn -> do
+    it "Decodes NULL into Nothing for Maybes" $ \conn -> do
       Just result <- LibPQ.execParams conn "SELECT NULL AS a" [] LibPQ.Text
 
       row <- Opium.fromRow (LibPQ.Row 0) result
       row `shouldBe` Right (MaybeTest Nothing)
 
-    it "decodes values into Just for Maybes" $ \conn -> do
+    it "Decodes values into Just for Maybes" $ \conn -> do
       Just result <- LibPQ.execParams conn "SELECT 'abc' AS a" [] LibPQ.Text
 
       row <- Opium.fromRow (LibPQ.Row 0) result
       row `shouldBe` Right (MaybeTest $ Just "abc")
 
   describe "fetch_" $ do
-    it "retrieves a list of rows" $ \conn -> do
+    it "Retrieves a list of rows" $ \conn -> do
       rows <- Opium.fetch_ conn "SELECT * FROM person"
       rows `shouldBe` Right [Person "paul" 25, Person "albus" 103]
 
-    it "fails for invalid queries" $ \conn -> do
+    it "Fails for invalid queries" $ \conn -> do
       rows <- Opium.fetch_ @Person conn "MRTLBRNFT"
       rows `shouldSatisfy` isLeft
 
-    it "fails for missing columns" $ \conn -> do
-      rows <- Opium.fetch_ @Person conn "SELECT name FROM person"
-      rows `shouldBe` Left (Opium.ErrorMissingColumn "age")
-
-    it "fails for unexpected NULLs" $ \conn -> do
+    it "Fails for unexpected NULLs" $ \conn -> do
       rows <- Opium.fetch_ @Person conn "SELECT NULL AS name, 0 AS age"
       rows `shouldBe` Left (Opium.ErrorUnexpectedNull (LibPQ.Row 0) "name")
 
-    it "fails for the wrong column type" $ \conn -> do
+    it "Fails for the wrong column type" $ \conn -> do
       rows <- Opium.fetch_ @Person conn "SELECT 'quby' AS name, 'indeterminate' AS age"
       rows `shouldBe` Left (Opium.ErrorDecode (LibPQ.Row 0) "age" $ Opium.FieldErrorInvalidOid $ LibPQ.Oid 25)