support custom types in query result scanning

CHANGELOG.md

@@ -1,5 +1,6 @@
 * Fixed potential infinity loop for local dc detection
 * Fixed nil pointer dereferenced in a topic listener
+* Added support of custom types to row.ScanStruct using sql.Scanner.Scan or UnmarshalYDBValue
 
 ## v3.99.2
 * Fixed panic when error returned from parsing sql params

internal/value/cast.go

@@ -1,5 +1,12 @@
 package value
 
+import (
+	"database/sql"
+	"database/sql/driver"
+
+	"github.com/google/uuid"
+)
+
 func CastTo(v Value, dst interface{}) error {
 	if dst == nil {
 		return errNilDestination
@@ -10,5 +17,28 @@ func CastTo(v Value, dst interface{}) error {
 		return nil
 	}
 
+	if _, ok := dst.(*uuid.UUID); ok {
+		return v.castTo(dst)
+	}
+
+	if scanner, has := dst.(sql.Scanner); has {
+		dv := new(driver.Value)
+
+		err := v.castTo(dv)
+		if err != nil {
+			return err
+		}
+
+		return scanner.Scan(*dv)
+	}
+
+	if scanner, has := dst.(Scanner); has {
+		return scanner.UnmarshalYDBValue(v)
+	}
+
 	return v.castTo(dst)
 }
+
+type Scanner interface {
+	UnmarshalYDBValue(value Value) error
+}

internal/value/cast_test.go

@@ -2,6 +2,7 @@ package value
 
 import (
 	"database/sql/driver"
+	"errors"
 	"reflect"
 	"testing"
 	"time"
@@ -32,6 +33,34 @@ func loadLocation(t *testing.T, name string) *time.Location {
 	return loc
 }
 
+type testStringValueScanner string
+
+func (s *testStringValueScanner) UnmarshalYDBValue(v Value) error {
+	var tmp string
+
+	err := CastTo(v, &tmp)
+	if err != nil {
+		return err
+	}
+
+	*s = testStringValueScanner(tmp)
+
+	return nil
+}
+
+type testStringSQLScanner string
+
+func (s *testStringSQLScanner) Scan(value any) error {
+	ts, ok := value.(string)
+	if !ok {
+		return errors.New("can't cast from " + reflect.TypeOf(value).String() + " to string")
+	}
+
+	*s = testStringSQLScanner(ts)
+
+	return nil
+}
+
 func TestCastTo(t *testing.T) {
 	testsCases := []struct {
 		name  string
@@ -428,6 +457,20 @@ func TestCastTo(t *testing.T) {
 			exp:   DateValueFromTime(time.Date(2024, 1, 2, 0, 0, 0, 0, time.UTC)),
 			err:   nil,
 		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: TextValue("text-string"),
+			dst:   ptr[testStringValueScanner](),
+			exp:   testStringValueScanner("text-string"),
+			err:   nil,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: TextValue("text-string"),
+			dst:   ptr[testStringSQLScanner](),
+			exp:   testStringSQLScanner("text-string"),
+			err:   nil,
+		},
 	}
 	for _, tt := range testsCases {
 		t.Run(tt.name, func(t *testing.T) {

internal/value/value.go

@@ -1303,7 +1303,7 @@ func (v *listValue) castTo(dst any) error {
 		inner.Set(newSlice)
 
 		for i, item := range v.ListItems() {
-			if err := item.castTo(inner.Index(i).Addr().Interface()); err != nil {
+			if err := CastTo(item, inner.Index(i).Addr().Interface()); err != nil {
 				return xerrors.WithStackTrace(fmt.Errorf(
 					"%w '%s(%+v)' to '%T' destination",
 					ErrCannotCast, v.Type().Yql(), v, dstValue,
@@ -1437,7 +1437,7 @@ func (v *setValue) castTo(dst any) error {
 		inner.Set(newSlice)
 
 		for i, item := range v.items {
-			if err := item.castTo(inner.Index(i).Addr().Interface()); err != nil {
+			if err := CastTo(item, inner.Index(i).Addr().Interface()); err != nil {
 				return xerrors.WithStackTrace(fmt.Errorf(
 					"%w '%s(%+v)' to '%T' destination",
 					ErrCannotCast, v.Type().Yql(), v, dstValue,
@@ -1545,7 +1545,7 @@ func (v *optionalValue) castTo(dst any) error {
 			return nil
 		}
 
-		if err := v.value.castTo(ptr.Interface()); err != nil {
+		if err := CastTo(v.value, (ptr.Interface())); err != nil {
 			return xerrors.WithStackTrace(err)
 		}
 
@@ -1560,7 +1560,7 @@ func (v *optionalValue) castTo(dst any) error {
 
 	inner.Set(reflect.New(inner.Type().Elem()))
 
-	if err := v.value.castTo(inner.Interface()); err != nil {
+	if err := CastTo(v.value, inner.Interface()); err != nil {
 		return xerrors.WithStackTrace(err)
 	}
 
@@ -1641,7 +1641,7 @@ func (v *structValue) castTo(dst any) error {
 		}
 
 		for i, field := range v.fields {
-			if err := field.V.castTo(inner.Field(i).Addr().Interface()); err != nil {
+			if err := CastTo(field.V, inner.Field(i).Addr().Interface()); err != nil {
 				return xerrors.WithStackTrace(fmt.Errorf(
 					"scan error on struct field name '%s': %w",
 					field.Name, err,
@@ -1768,7 +1768,7 @@ func (v *tupleValue) TupleItems() []Value {
 
 func (v *tupleValue) castTo(dst any) error {
 	if len(v.items) == 1 {
-		return v.items[0].castTo(dst)
+		return CastTo(v.items[0], dst)
 	}
 
 	switch dstValue := dst.(type) {

tests/integration/query_range_test.go

@@ -17,8 +17,17 @@ import (
 	"github.com/ydb-platform/ydb-go-sdk/v3/internal/value"
 	"github.com/ydb-platform/ydb-go-sdk/v3/internal/xtest"
 	"github.com/ydb-platform/ydb-go-sdk/v3/query"
+	"github.com/ydb-platform/ydb-go-sdk/v3/table/types"
 )
 
+type testStringValueScanner struct {
+	field string
+}
+
+func (v *testStringValueScanner) UnmarshalYDBValue(value types.Value) error {
+	return types.CastTo(value, &v.field)
+}
+
 func TestQueryRange(t *testing.T) {
 	ctx, cancel := context.WithCancel(xtest.Context(t))
 	defer cancel()
@@ -84,19 +93,22 @@ func TestQueryRange(t *testing.T) {
 			p1 string
 			p2 uint64
 			p3 time.Duration
+			p4 testStringValueScanner
 		)
 		err := db.Query().Do(ctx, func(ctx context.Context, s query.Session) error {
 			r, err := s.Query(ctx, `
 				DECLARE $p1 AS Text;
 				DECLARE $p2 AS Uint64;
 				DECLARE $p3 AS Interval;
-				SELECT $p1, $p2, $p3;
+				DECLARE $p4 AS Text;
+				SELECT $p1, $p2, $p3, $p4;
 			`,
 				query.WithParameters(
 					ydb.ParamsBuilder().
 						Param("$p1").Text("test").
 						Param("$p2").Uint64(100500000000).
 						Param("$p3").Interval(time.Duration(100500000000)).
+						Param("$p4").Text("test2").
 						Build(),
 				),
 				query.WithSyntax(query.SyntaxYQL),
@@ -112,7 +124,7 @@ func TestQueryRange(t *testing.T) {
 					if err != nil {
 						return err
 					}
-					err = row.Scan(&p1, &p2, &p3)
+					err = row.Scan(&p1, &p2, &p3, &p4)
 					if err != nil {
 						return err
 					}
@@ -126,6 +138,9 @@ func TestQueryRange(t *testing.T) {
 					if p3 != time.Duration(100500000000) {
 						return fmt.Errorf("unexpected p3 value: %v", p3)
 					}
+					if p4.field != "test2" {
+						return fmt.Errorf("unexpected p4 value: %v", p4)
+					}
 				}
 			}
 			return nil