Add errors and optional fields

test/Database/PostgreSQL/Opium/FromFieldSpec.hs

@@ -32,8 +32,8 @@ instance FromRow SingleString where
 
 shouldFetch :: (Eq a, FromRow a, Show a) => Connection -> ByteString -> [a] -> IO ()
 shouldFetch conn query expectedRows = do
-  Just actualRows <- Opium.fetch_ conn query
-  actualRows `shouldBe` expectedRows
+  actualRows <- Opium.fetch_ conn query
+  actualRows `shouldBe` Right expectedRows
 
 spec :: SpecWith Connection
 spec = do

test/Database/PostgreSQL/OpiumSpec.hs

@@ -7,7 +7,7 @@ module Database.PostgreSQL.OpiumSpec (spec) where
 import Data.Text (Text)
 import Database.PostgreSQL.LibPQ (Connection)
 import GHC.Generics (Generic)
-import Test.Hspec (SpecWith, describe, it, shouldBe)
+import Test.Hspec (SpecWith, describe, it, shouldBe, shouldSatisfy)
 
 import qualified Database.PostgreSQL.LibPQ as LibPQ
 import qualified Database.PostgreSQL.Opium as Opium
@@ -19,6 +19,16 @@ data Person = Person
 
 instance Opium.FromRow Person where
 
+newtype MaybeTest = MaybeTest
+  { a :: Maybe String
+  } deriving (Eq, Generic, Show)
+
+instance Opium.FromRow MaybeTest where
+
+isLeft :: Either a b -> Bool
+isLeft (Left _) = True
+isLeft _ = False
+
 spec :: SpecWith Connection
 spec = do
   describe "fromRow" $ do
@@ -26,12 +36,40 @@ spec = do
       Just result <- LibPQ.execParams conn "SELECT * FROM person" [] LibPQ.Text
 
       row0 <- Opium.fromRow @Person (LibPQ.Row 0) result
-      row0 `shouldBe` Just (Person "paul" 25)
+      row0 `shouldBe` Right (Person "paul" 25)
 
       row1 <- Opium.fromRow @Person (LibPQ.Row 1) result
-      row1 `shouldBe` Just (Person "albus" 103)
+      row1 `shouldBe` Right (Person "albus" 103)
+
+    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
+      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
       rows <- Opium.fetch_ conn "SELECT * FROM person"
-      rows `shouldBe` Just [Person "paul" 25, Person "albus" 103]
+      rows `shouldBe` Right [Person "paul" 25, Person "albus" 103]
+
+    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
+      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
+      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)