jackc/pgx · error

cannot scan into non-pointer or nil destinations %T

Error message

cannot scan into non-pointer or nil destinations %T

What it means

This guard in the JSONUnmarshal scan plan verifies that the destination passed to Scan is a non-nil Go pointer before reflection is used to set it. It fires when dst is not a pointer at all, or is a nil pointer, making assignment impossible; the offending destination type is included in the message.

Solutions

1. Always pass the address of the target variable (e.g. &myValue) to Scan
2. Ensure the destination pointer is initialized and non-nil before scanning
3. Check the variable declaration for a missing & operator

When it happens

Trigger: Thrown at pgtype/json.go:216 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: /api/errors/39f64572b26566f4. Report an issue: GitHub.

Appendix: source

Thrown at pgtype/json.go:216

func (s *scanPlanJSONToJSONUnmarshal) Scan(src []byte, dst any) error {
	if src == nil {
		dstValue := reflect.ValueOf(dst)
		if dstValue.Kind() == reflect.Pointer {
			el := dstValue.Elem()
			switch el.Kind() {
			case reflect.Pointer, reflect.Slice, reflect.Map, reflect.Interface:
				el.Set(reflect.Zero(el.Type()))
				return nil
			}
		}

		return fmt.Errorf("cannot scan NULL into %T", dst)
	}

	v := reflect.ValueOf(dst)
	if v.Kind() != reflect.Pointer || v.IsNil() {
		return fmt.Errorf("cannot scan into non-pointer or nil destinations %T", dst)
	}

	elem := v.Elem()
	elem.Set(reflect.Zero(elem.Type()))

	return s.unmarshal(src, dst)
}

func (c *JSONCodec) DecodeDatabaseSQLValue(m *Map, oid uint32, format int16, src []byte) (driver.Value, error) {
	if src == nil {
		return nil, nil
	}

	dstBuf := make([]byte, len(src))
	copy(dstBuf, src)
	return dstBuf, nil
}

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