Add getColumnTable function

test/Database/PostgreSQL/OpiumSpec.hs

@@ -4,6 +4,7 @@
 
 module Database.PostgreSQL.OpiumSpec (spec) where
 
+import Data.Proxy (Proxy (..))
 import Data.Text (Text)
 import Database.PostgreSQL.LibPQ (Connection)
 import GHC.Generics (Generic)
@@ -31,6 +32,21 @@ isLeft _ = False
 
 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 (Proxy :: Proxy Person) result
+      columnTable `shouldBe` [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]
+
+      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]
+
   describe "fromRow" $ do
     it "decodes rows in a Result" $ \conn -> do
       Just result <- LibPQ.execParams conn "SELECT * FROM person" [] LibPQ.Text