Merge pull request #1283 from ydb-platform/err-description

added description to error message if scan failed

Author: asmyasnikov

CHANGELOG.md

@@ -1,3 +1,5 @@
+* Added description to scan errors with use query service client scanner
+
 ## v3.74.1
 * Allowed the use of DSN without specifying the protocol/scheme
 * Allowed casts from signed YDB types to unsigned destination types if source value is not negative

internal/query/scanner/indexed.go

@@ -29,7 +29,7 @@ func (s IndexedScanner) Scan(dst ...interface{}) (err error) {
 	for i := range dst {
 		v := s.data.seekByIndex(i)
 		if err := value.CastTo(v, dst[i]); err != nil {
-			return xerrors.WithStackTrace(err)
+			return xerrors.WithStackTrace(fmt.Errorf("scan error on column index %d: %w", i, err))
 		}
 	}
 

internal/query/scanner/indexed_test.go

@@ -556,3 +556,28 @@ func TestIndexedCastFailed(t *testing.T) {
 	err := scanner.Scan(&A)
 	require.ErrorIs(t, err, value.ErrCannotCast)
 }
+
+func TestIndexedCastFailedErrMsg(t *testing.T) {
+	scanner := Indexed(Data(
+		[]*Ydb.Column{
+			{
+				Name: "a",
+				Type: &Ydb.Type{
+					Type: &Ydb.Type_TypeId{
+						TypeId: Ydb.Type_UTF8,
+					},
+				},
+			},
+		},
+		[]*Ydb.Value{
+			{
+				Value: &Ydb.Value_TextValue{
+					TextValue: "test",
+				},
+			},
+		},
+	))
+	var A uint64
+	err := scanner.Scan(&A)
+	require.ErrorContains(t, err, "scan error on column index 0: cast failed")
+}

internal/query/scanner/named.go

@@ -57,7 +57,7 @@ func (s NamedScanner) ScanNamed(dst ...NamedDestination) (err error) {
 			return xerrors.WithStackTrace(err)
 		}
 		if err = value.CastTo(v, dst[i].Ref()); err != nil {
-			return xerrors.WithStackTrace(err)
+			return xerrors.WithStackTrace(fmt.Errorf("scan error on column name '%s': %w", dst[i].Name(), err))
 		}
 	}
 

internal/query/scanner/named_test.go

@@ -699,3 +699,28 @@ func TestNamedCastFailed(t *testing.T) {
 	err := scanner.ScanNamed(NamedRef("a", &A))
 	require.ErrorIs(t, err, value.ErrCannotCast)
 }
+
+func TestNamedCastFailedErrMsg(t *testing.T) {
+	scanner := Named(Data(
+		[]*Ydb.Column{
+			{
+				Name: "a",
+				Type: &Ydb.Type{
+					Type: &Ydb.Type_TypeId{
+						TypeId: Ydb.Type_UTF8,
+					},
+				},
+			},
+		},
+		[]*Ydb.Value{
+			{
+				Value: &Ydb.Value_TextValue{
+					TextValue: "test",
+				},
+			},
+		},
+	))
+	var A uint64
+	err := scanner.ScanNamed(NamedRef("a", &A))
+	require.ErrorContains(t, err, "scan error on column name 'a': cast failed")
+}

internal/query/scanner/struct.go

@@ -61,7 +61,7 @@ func (s StructScanner) ScanStruct(dst interface{}, opts ...ScanStructOption) (er
 			missingColumns = append(missingColumns, name)
 		} else {
 			if err = value.CastTo(v, ptr.Elem().Field(i).Addr().Interface()); err != nil {
-				return xerrors.WithStackTrace(err)
+				return xerrors.WithStackTrace(fmt.Errorf("scan error on struct field name '%s': %w", name, err))
 			}
 			existingFields[name] = struct{}{}
 		}

internal/query/scanner/struct_test.go

@@ -563,6 +563,33 @@ func TestStructCastFailed(t *testing.T) {
 	require.ErrorIs(t, err, value.ErrCannotCast)
 }
 
+func TestStructCastFailedErrMsg(t *testing.T) {
+	scanner := Struct(Data(
+		[]*Ydb.Column{
+			{
+				Name: "A",
+				Type: &Ydb.Type{
+					Type: &Ydb.Type_TypeId{
+						TypeId: Ydb.Type_UTF8,
+					},
+				},
+			},
+		},
+		[]*Ydb.Value{
+			{
+				Value: &Ydb.Value_TextValue{
+					TextValue: "test",
+				},
+			},
+		},
+	))
+	var row struct {
+		A uint64
+	}
+	err := scanner.ScanStruct(&row)
+	require.ErrorContains(t, err, "scan error on struct field name 'A': cast failed")
+}
+
 func TestStructNotFoundColumns(t *testing.T) {
 	scanner := Struct(Data(
 		[]*Ydb.Column{

internal/value/errors.go

@@ -3,7 +3,7 @@ package value
 import "errors"
 
 var (
-	ErrCannotCast                   = errors.New("cannot cast")
+	ErrCannotCast                   = errors.New("cast failed")
 	errDestinationTypeIsNotAPointer = errors.New("destination type is not a pointer")
 	errNilDestination               = errors.New("destination is nil")
 )