README: add query usage example

README.md

@@ -18,33 +18,33 @@ module Test.Example where
 
 import Prelude
 
-import Database.PostgreSQL (defaultPoolConfiguration, execute, newPool, Query(Query), withConnection)
+import Database.PostgreSQL (defaultPoolConfiguration, execute, newPool, query, Query(Query), withConnection)
 import Database.PostgreSQL.Row (Row0(Row0), Row3(Row3))
 import Data.Decimal as Decimal
 import Data.Maybe (Maybe(..))
 import Data.Tuple.Nested ((/\))
 import Effect.Aff (Aff)
+import Effect.Class (liftEffect)
+import Test.Assert (assert)
 
 -- Our interaction with db is performed asynchronously in `Aff`
 run ∷ Aff Unit
 run = do
 
-  -- Now we are able to setup connection. We are assuming here
+  -- We assume here that postgres is running on a standard local port together
-  -- that postgres is running on a standard local port.
+  -- with `ident` authentication so configuration can be nearly empty.
-  -- We use `ident` authentication so configuration can be nearly empty.
   -- It requires only database name which we pass to `newPool` function.
-  -- We want to close connection after a second (`idleTimeoutMillis` setting) because this code
+  -- We setup also `idleTimeoutMillis` setting because this code
-  -- would be run by our test suite ;-)
+  -- would be run by our test suite and we want to finish quickly ;-)
-  -- Of course you can provide additional configuration settings if you need to.
 
   pool <- newPool ((defaultPoolConfiguration "purspg") { idleTimeoutMillis = Just 1000 })
   withConnection pool \conn -> do
 
     -- We can now create our temporary table which we are going to query in this example.
-    -- `execute` performs this query. It ignores result value by default.
+    -- `execute` ignores result value which is what we want in this case.
  
     execute conn (Query """
-      CREATE TEMPORARY TABLE foods (
+      CREATE TEMPORARY TABLE fruits (
         name text NOT NULL,
         delicious boolean NOT NULL,
         price NUMERIC(4,2) NOT NULL,
@@ -60,18 +60,28 @@ run = do
     -- provides instances for automatic conversions from and to SQL values.
 
     execute conn (Query """
-      INSERT INTO foods (name, delicious, price)
+      INSERT INTO fruits (name, delicious, price)
       VALUES ($1, $2, $3)
-    """) (Row3 "pork" true (Decimal.fromString "8.30"))
+    """) (Row3 "coconut" true (Decimal.fromString "8.30"))
 
 
     -- You can also use nested tuples instead of `Row*` types but this can be a bit more
     -- verbose. `/\` is just an alias for `Tuple` constructor.
 
     execute conn (Query """
-      INSERT INTO foods (name, delicious, price)
+      INSERT INTO fruits (name, delicious, price)
       VALUES ($1, $2, $3)
-    """) ("sauerkraut" /\ false /\ Decimal.fromString "3.30")
+    """) ("lemon" /\ false /\ Decimal.fromString "3.30")
+
+    -- Of course `Row*` typees and nested tuples can be also used when we are fetching
+    -- data from db.
+
+    names <- query conn (Query """
+      SELECT name, delicious
+      FROM fruits
+      ORDER BY name ASC
+    """) Row0
+    liftEffect <<< assert $ names == ["coconut" /\ true, "lemon" /\ false]
 
 ```
 

src/Database/PostgreSQL/Row.purs

@@ -20,7 +20,9 @@ class FromSQLRow a where
 instance toSQLRowForeignArray :: ToSQLRow (Array Foreign) where
   toSQLRow = identity
 
-instance toSQLRowTuple :: (ToSQLValue a, ToSQLRow (Tuple b t)) => ToSQLRow (Tuple a (Tuple b t)) where
+instance toSQLRowTupleOfTuples :: (ToSQLRow (Tuple a ta), ToSQLRow (Tuple b t)) => ToSQLRow (Tuple (Tuple a ta) (Tuple b t)) where
+  toSQLRow (Tuple a t) = toSQLRow a <> toSQLRow t
+else instance toSQLRowTuple :: (ToSQLValue a, ToSQLRow (Tuple b t)) => ToSQLRow (Tuple a (Tuple b t)) where
   toSQLRow (Tuple a t) = toSQLValue a : toSQLRow t
 else instance toSQLRowTupleEnd :: (ToSQLValue a, ToSQLValue b) => ToSQLRow (Tuple a b) where
   toSQLRow (Tuple a b) = [ toSQLValue a, toSQLValue b ]

test/Main.purs

@@ -128,9 +128,9 @@ main = do
               INSERT INTO foods (name, delicious, price)
               VALUES ($1, $2, $3), ($4, $5, $6), ($7, $8, $9)
             """)
-              ( "pork" /\ true /\ (D.fromString "8.30")
+              ( ("pork" /\ true /\ (D.fromString "8.30"))
-              /\ "sauerkraut" /\ false /\ (D.fromString "3.30")
+              /\ ("sauerkraut" /\ false /\ (D.fromString "3.30"))
-              /\ "rookworst" /\ true /\ (D.fromString "5.60"))
+              /\ ("rookworst" /\ true /\ (D.fromString "5.60")))
             names <- query conn (Query """
               SELECT name, delicious
               FROM foods