jackc/pgx · error

got %d values, but dst struct has only %d fields

Error message

got %d values, but dst struct has only %d fields

What it means

Error "got %d values, but dst struct has only %d fields" thrown in jackc/pgx.

Source

Thrown at rows.go:589

// RowToAddrOfStructByPos returns the address of a T scanned from row. T must be a struct. T must have the same number a
// public fields as row has fields. The row and T fields will be matched by position. If the "db" struct tag is "-" then
// the field will be ignored.
func RowToAddrOfStructByPos[T any](row CollectableRow) (*T, error) {
	var value T
	err := (&positionalStructRowScanner{ptrToStruct: &value}).ScanRow(row)
	return &value, err
}

type positionalStructRowScanner struct {
	ptrToStruct any
}

func (rs *positionalStructRowScanner) ScanRow(rows CollectableRow) error {
	typ := reflect.TypeOf(rs.ptrToStruct).Elem()
	fields := lookupStructFields(typ)
	if len(rows.RawValues()) > len(fields) {
		return fmt.Errorf(
			"got %d values, but dst struct has only %d fields",
			len(rows.RawValues()),
			len(fields),
		)
	}
	scanTargets := setupStructScanTargets(rs.ptrToStruct, fields)
	return rows.Scan(scanTargets...)
}

// Map from reflect.Type -> []structRowField
var positionalStructFieldMap sync.Map

func lookupStructFields(t reflect.Type) []structRowField {
	if cached, ok := positionalStructFieldMap.Load(t); ok {
		return cached.([]structRowField)
	}

	fieldStack := make([]int, 0, 1)

View on GitHub (pinned to ec1a0befd2)

When it happens

Trigger: Thrown at rows.go:589 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of jackc/pgx@ec1a0befd2 (2026-08-04). Data as JSON: /data/errors/17d0a78bfe3e0a1a.json. Report an issue: GitHub.