Additional scan performance improvements

Move typeStack to ScanContext, so it is shared between rows.Scan calls.
Use string.Builder for string concatenations.
Simplify value assign logic.
Move convert value to the last assign step (needs for type conversions are rare).

tests/postgres/scan_test.go

@@ -786,6 +786,123 @@ func TestRowsScan(t *testing.T) {
 	requireQueryLogged(t, stmt, 0)
 }
 
+func TestScanNullColumn(t *testing.T) {
+	stmt := SELECT(
+		Address.AllColumns,
+	).FROM(
+		Address,
+	).WHERE(
+		Address.Address2.IS_NULL(),
+	)
+
+	var dest []model.Address
+
+	err := stmt.Query(db, &dest)
+	require.NoError(t, err)
+	testutils.AssertJSON(t, dest, `
+[
+	{
+		"AddressID": 1,
+		"Address": "47 MySakila Drive",
+		"Address2": null,
+		"District": "Alberta",
+		"CityID": 300,
+		"PostalCode": "",
+		"Phone": "",
+		"LastUpdate": "2006-02-15T09:45:30Z"
+	},
+	{
+		"AddressID": 2,
+		"Address": "28 MySQL Boulevard",
+		"Address2": null,
+		"District": "QLD",
+		"CityID": 576,
+		"PostalCode": "",
+		"Phone": "",
+		"LastUpdate": "2006-02-15T09:45:30Z"
+	},
+	{
+		"AddressID": 3,
+		"Address": "23 Workhaven Lane",
+		"Address2": null,
+		"District": "Alberta",
+		"CityID": 300,
+		"PostalCode": "",
+		"Phone": "14033335568",
+		"LastUpdate": "2006-02-15T09:45:30Z"
+	},
+	{
+		"AddressID": 4,
+		"Address": "1411 Lillydale Drive",
+		"Address2": null,
+		"District": "QLD",
+		"CityID": 576,
+		"PostalCode": "",
+		"Phone": "6172235589",
+		"LastUpdate": "2006-02-15T09:45:30Z"
+	}
+]
+`)
+}
+
+func TestRowsScanSetZeroValue(t *testing.T) {
+	stmt := SELECT(
+		Rental.AllColumns,
+	).FROM(
+		Rental,
+	).WHERE(
+		Rental.RentalID.IN(Int(16049), Int(15966)),
+	).ORDER_BY(
+		Rental.RentalID.DESC(),
+	)
+
+	rows, err := stmt.Rows(context.Background(), db)
+	require.NoError(t, err)
+
+	defer rows.Close()
+
+	// destination object is used as destination for all rows scan.
+	// this tests checks that ReturnedDate is set to nil with the second call
+	// check qrm.setZeroValue
+	var dest model.Rental
+
+	for rows.Next() {
+		err := rows.Scan(&dest)
+		require.NoError(t, err)
+
+		if dest.RentalID == 16049 {
+			testutils.AssertJSON(t, dest, `
+{
+	"RentalID": 16049,
+	"RentalDate": "2005-08-23T22:50:12Z",
+	"InventoryID": 2666,
+	"CustomerID": 393,
+	"ReturnDate": "2005-08-30T01:01:12Z",
+	"StaffID": 2,
+	"LastUpdate": "2006-02-16T02:30:53Z"
+}
+`)
+		} else {
+			testutils.AssertJSON(t, dest, `
+{
+	"RentalID": 15966,
+	"RentalDate": "2006-02-14T15:16:03Z",
+	"InventoryID": 4472,
+	"CustomerID": 374,
+	"ReturnDate": null,
+	"StaffID": 1,
+	"LastUpdate": "2006-02-16T02:30:53Z"
+}
+`)
+		}
+	}
+
+	err = rows.Close()
+	require.NoError(t, err)
+	err = rows.Err()
+	require.NoError(t, err)
+}
+
 func TestScanNumericToFloat(t *testing.T) {
 	type Number struct {
 		Float32 float32
@@ -826,6 +943,54 @@ func TestScanNumericToIntegerError(t *testing.T) {
 
 }
 
+func TestScanIntoCustomBaseTypes(t *testing.T) {
+
+	type MyUint8 uint8
+	type MyUint16 uint16
+	type MyUint32 uint32
+	type MyInt16 int16
+	type MyFloat32 float32
+	type MyFloat64 float64
+	type MyString string
+	type MyTime = time.Time
+
+	type film struct {
+		FilmID          MyUint16 `sql:"primary_key"`
+		Title           MyString
+		Description     *MyString
+		ReleaseYear     *MyInt16
+		LanguageID      MyUint8
+		RentalDuration  MyUint8
+		RentalRate      MyFloat32
+		Length          *MyUint32
+		ReplacementCost MyFloat64
+		Rating          *model.MpaaRating
+		LastUpdate      MyTime
+		SpecialFeatures *MyString
+		Fulltext        MyString
+	}
+
+	stmt := SELECT(
+		Film.AllColumns,
+	).FROM(
+		Film,
+	).ORDER_BY(
+		Film.FilmID.ASC(),
+	).LIMIT(3)
+
+	var films []model.Film
+
+	err := stmt.Query(db, &films)
+	require.NoError(t, err)
+
+	var myFilms []film
+
+	err = stmt.Query(db, &myFilms)
+	require.NoError(t, err)
+
+	require.Equal(t, testutils.ToJSON(films), testutils.ToJSON(myFilms))
+}
+
 // QueryContext panic when the scanned value is nil and the destination is a slice of primitive
 // https://github.com/go-jet/jet/issues/91
 func TestScanToPrimitiveElementsSlice(t *testing.T) {