Make Connection parameter go last in query functions

README.md

@@ -33,8 +33,8 @@ data User = User
 
 instance Opium.FromRow User where
 
-getUsers :: Connection -> IO (Either Opium.Error [Users])
-getUsers conn = Opium.fetch_ conn "SELECT * FROM user"
+getUsers :: Connection -> IO (Either Opium.Error [User])
+getUsers conn = Opium.fetch_ "SELECT * FROM user" conn
 ```
 
 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_ conn query
+  Right [x] <- Opium.fetch_ query conn
   pure x
 ```
 

lib/Database/PostgreSQL/Opium.hs

@@ -6,6 +6,9 @@
 module Database.PostgreSQL.Opium
     -- * Queries
     --
+    -- Functions for performing queries. @fetch@ retrieves rows, @execute@ doesn't.
+    -- The 'Connection' parameter comes last to facilitate currying for implicitly passing in the connection, e.g. from some framework's connection pool.
+    --
     -- | TODO: Add @newtype Query = Query Text@ with @IsString@ instance to make constructing query strings at run time harder.
   ( fetch
   , fetch_
@@ -45,29 +48,29 @@ import Database.PostgreSQL.Opium.ToParamList (ToParamList (..))
 -- The order of the type parameters is important, because it is more common to use type applications for providing the row type.
 fetch
   :: forall a b. (ToParamList b, FromRow a)
-  => Connection
-  -> Text
+  => Text
   -> b
+  -> Connection
   -> IO (Either Error [a])
-fetch conn query params = runExceptT $ do
+fetch query params conn = runExceptT $ do
   result <- execParams conn query params
   columnTable <- ExceptT $ getColumnTable @a Proxy result
   nRows <- liftIO $ LibPQ.ntuples result
   mapM (ExceptT . fromRow result columnTable) [0..nRows - 1]
 
-fetch_ :: forall a. FromRow a => Connection -> Text -> IO (Either Error [a])
-fetch_ conn query = fetch conn query ()
+fetch_ :: forall a. FromRow a => Text -> Connection -> IO (Either Error [a])
+fetch_ query = fetch query ()
 
 execute
   :: forall a. ToParamList a
-  => Connection
-  -> Text
+  => Text
   -> a
+  -> Connection
   -> IO (Either Error ())
-execute conn query params = runExceptT $ void $ execParams conn query params
+execute query params conn = runExceptT $ void $ execParams conn query params
 
-execute_ :: Connection -> Text -> IO (Either Error ())
-execute_ conn query = execute conn query ()
+execute_ :: Text -> Connection -> IO (Either Error ())
+execute_ query = execute query ()
 
 execParams
   :: ToParamList a

test/Database/PostgreSQL/Opium/FromFieldSpec.hs

@@ -115,7 +115,7 @@ instance FromRow ARawField where
 
 shouldFetch :: (Eq a, FromRow a, Show a) => Connection -> Text -> [a] -> IO ()
 shouldFetch conn query expectedRows = do
-  actualRows <- Opium.fetch_ conn query
+  actualRows <- Opium.fetch_ query conn
   actualRows `shouldBe` Right expectedRows
 
 (/\) :: (a -> Bool) -> (a -> Bool) -> a -> Bool
@@ -213,15 +213,15 @@ spec = do
       shouldFetch conn "SELECT 4.2::real AS float" [AFloat 4.2]
 
     it "Decodes NaN::real" $ \conn -> do
-      Right [AFloat value] <- Opium.fetch_ conn "SELECT 'NaN'::real AS float"
+      Right [AFloat value] <- Opium.fetch_ "SELECT 'NaN'::real AS float" conn
       value `shouldSatisfy` isNaN
 
     it "Decodes Infinity::real" $ \conn -> do
-      Right [AFloat value] <- Opium.fetch_ conn "SELECT 'Infinity'::real AS float"
+      Right [AFloat value] <- Opium.fetch_ "SELECT 'Infinity'::real AS float" conn
       value `shouldSatisfy` (isInfinite /\ (> 0))
 
     it "Decodes -Infinity::real" $ \conn -> do
-      Right [AFloat value] <- Opium.fetch_ conn "SELECT '-Infinity'::real AS float"
+      Right [AFloat value] <- Opium.fetch_ "SELECT '-Infinity'::real AS float" conn
       value `shouldSatisfy` (isInfinite /\ (< 0))
 
   describe "FromField Double" $ do
@@ -229,22 +229,22 @@ spec = do
       shouldFetch conn "SELECT 4.2::double precision AS double" [ADouble 4.2]
 
     it "Decodes NaN::double precision" $ \conn -> do
-      Right [ADouble value] <- Opium.fetch_ conn "SELECT 'NaN'::double precision AS double"
+      Right [ADouble value] <- Opium.fetch_ "SELECT 'NaN'::double precision AS double" conn
       value `shouldSatisfy` isNaN
 
     it "Decodes Infinity::double precision" $ \conn -> do
-      Right [ADouble value] <- Opium.fetch_ conn "SELECT 'Infinity'::double precision AS double"
+      Right [ADouble value] <- Opium.fetch_ "SELECT 'Infinity'::double precision AS double" conn
       value `shouldSatisfy` (isInfinite /\ (> 0))
 
     it "Decodes -Infinity::double precision" $ \conn -> do
-      Right [ADouble value] <- Opium.fetch_ conn "SELECT '-Infinity'::double precision AS double"
+      Right [ADouble value] <- Opium.fetch_ "SELECT '-Infinity'::double precision AS double" conn
       value `shouldSatisfy` (isInfinite /\ (< 0))
 
     it "Decodes {inf,-inf}::double precision" $ \conn -> do
-      Right [ADouble value0] <- Opium.fetch_ conn "SELECT 'inf'::double precision AS double"
+      Right [ADouble value0] <- Opium.fetch_ "SELECT 'inf'::double precision AS double" conn
       value0 `shouldSatisfy` (isInfinite /\ (> 0))
 
-      Right [ADouble value1] <- Opium.fetch_ conn "SELECT '-inf'::double precision AS double"
+      Right [ADouble value1] <- Opium.fetch_ "SELECT '-inf'::double precision AS double" conn
       value1 `shouldSatisfy` (isInfinite /\ (< 0))
 
   describe "FromField Bool" $ do

test/Database/PostgreSQL/OpiumSpec.hs

@@ -124,30 +124,30 @@ spec = do
 
   describe "fetch" $ do
     it "Passes numbered parameters and retrieves a list of rows" $ \conn -> do
-      rows <- Opium.fetch conn "SELECT ($1 + $2) AS only" (17 :: Int, 25 :: Int)
+      rows <- Opium.fetch "SELECT ($1 + $2) AS only" (17 :: Int, 25 :: Int) conn
       rows `shouldBe` Right [Only (42 :: Int)]
 
     it "Uses Identity to pass single parameters" $ \conn -> do
-      rows <- Opium.fetch conn "SELECT count(*) AS only FROM person WHERE name = $1" $ Identity ("paul" :: Text)
+      rows <- Opium.fetch "SELECT count(*) AS only FROM person WHERE name = $1" (Identity ("paul" :: Text)) conn
       rows `shouldBe` Right [Only (1 :: Int)]
 
   describe "fetch_" $ do
     it "Retrieves a list of rows" $ \conn -> do
-      rows <- Opium.fetch_ conn "SELECT * FROM person"
+      rows <- Opium.fetch_ "SELECT * FROM person" conn
       rows `shouldBe` Right [Person "paul" 25, Person "albus" 103]
 
     it "Fails for invalid queries" $ \conn -> do
-      rows <- Opium.fetch_ @Person conn "MRTLBRNFT"
+      rows <- Opium.fetch_ @Person "MRTLBRNFT" conn
       rows `shouldSatisfy` isLeft
 
     it "Fails for unexpected NULLs" $ \conn -> do
-      rows <- Opium.fetch_ @Person conn "SELECT NULL AS name, 0 AS age"
+      rows <- Opium.fetch_ @Person "SELECT NULL AS name, 0 AS age" conn
       rows `shouldBe` Left (Opium.ErrorUnexpectedNull (Opium.ErrorPosition 0 "name"))
 
     it "Fails for the wrong column type" $ \conn -> do
-      rows <- Opium.fetch_ @Person conn "SELECT 'quby' AS name, 'indeterminate' AS age"
+      rows <- Opium.fetch_ @Person "SELECT 'quby' AS name, 'indeterminate' AS age" conn
       rows `shouldBe` Left (Opium.ErrorInvalidOid "age" $ LibPQ.Oid 25)
 
     it "Works for the readme regression example" $ \conn -> do
-      rows <- Opium.fetch_ @ScoreByAge conn "SELECT regr_intercept(score, age) AS t, regr_slope(score, age) AS m FROM person"
+      rows <- Opium.fetch_ @ScoreByAge "SELECT regr_intercept(score, age) AS t, regr_slope(score, age) AS m FROM person" conn
       rows `shouldSatisfy` \case { (Right [ScoreByAge _ _]) -> True; _ -> False }