Use Vector for column table for constant element access

test/Database/PostgreSQL/OpiumSpec.hs

@@ -5,6 +5,7 @@
 
 module Database.PostgreSQL.OpiumSpec (spec) where
 
+import Data.ByteString (ByteString)
 import Data.Proxy (Proxy (..))
 import Data.Text (Text)
 import Database.PostgreSQL.LibPQ (Connection)
@@ -41,22 +42,35 @@ isLeft :: Either a b -> Bool
 isLeft (Left _) = True
 isLeft _ = False
 
+shouldHaveColumns
+  :: Opium.FromRow a
+  => Proxy a
+  -> Connection
+  -> ByteString
+  -> [LibPQ.Column]
+  -> IO ()
+shouldHaveColumns proxy conn query expectedColumns = do
+  Just result <- LibPQ.execParams conn query [] LibPQ.Text
+  columnTable <- Opium.getColumnTable proxy result
+  let actualColumns = fmap (map fst . Opium.toListColumnTable) columnTable
+  actualColumns `shouldBe` Right expectedColumns
+
 spec :: SpecWith Connection
 spec = do
   describe "getColumnTable" $ 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
-      fmap (map fst) columnTable `shouldBe` Right [0, 1]
+      shouldHaveColumns @Person Proxy conn
+        "SELECT name, age FROM person"
+        [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
-      fmap (map fst) columnTable0 `shouldBe` Right [1, 0]
+      shouldHaveColumns @Person Proxy conn
+        "SELECT age, name FROM person"
+        [1, 0]
 
-      Just result1 <- LibPQ.execParams conn "SELECT 0 AS a, 1 AS b, 2 AS c, age, 4 AS d, name FROM person" [] LibPQ.Text
-      columnTable1 <- Opium.getColumnTable @Person Proxy result1
-      fmap (map fst) columnTable1 `shouldBe` Right [5, 3]
+      shouldHaveColumns @Person Proxy conn
+        "SELECT 0 AS a, 1 AS b, 2 AS c, age, 4 AS d, name FROM person"
+        [5, 3]
 
     it "Fails for missing columns" $ \conn -> do
       Just result <- LibPQ.execParams conn "SELECT 0 AS a FROM person" [] LibPQ.Text