hyperledger/fabric · error

expected key %s/fields/%s/%s to encode a value of type Strin

Error message

expected key %s/fields/%s/%s to encode a value of type String, but was %T

What it means

Returned by Serializer.DeserializeFieldAsString when the stored StateData oneof is set but is not the String variant — e.g. an Int64 or Bytes was stored where the struct field expects a string. A type mismatch between the Go field and the encoded state.

Source

Thrown at core/chaincode/lifecycle/serializer.go:426

	err = proto.Unmarshal(value, stateData)
	if err != nil {
		return nil, errors.Wrapf(err, "could not unmarshal state for key %s", keyName)
	}

	return stateData, nil
}

func (s *Serializer) DeserializeFieldAsString(namespace, name, field string, state ReadableState) (string, error) {
	value, err := s.DeserializeField(namespace, name, field, state)
	if err != nil {
		return "", err
	}
	if value.Type == nil {
		return "", nil
	}
	oneOf, ok := value.Type.(*lb.StateData_String_)
	if !ok {
		return "", errors.Errorf("expected key %s/fields/%s/%s to encode a value of type String, but was %T", namespace, name, field, value.Type)
	}
	return oneOf.String_, nil
}

func (s *Serializer) DeserializeFieldAsBytes(namespace, name, field string, state ReadableState) ([]byte, error) {
	value, err := s.DeserializeField(namespace, name, field, state)
	if err != nil {
		return nil, err
	}
	if value.Type == nil {
		return nil, nil
	}
	oneOf, ok := value.Type.(*lb.StateData_Bytes)
	if !ok {
		return nil, errors.Errorf("expected key %s to encode a value of type []byte, but was %T", FieldKey(namespace, name, field), value.Type)
	}
	return oneOf.Bytes, nil
}

View on GitHub (pinned to 2736b63f8f)

Solutions

1. Ensure the field was committed as a string value
2. Re-commit the chaincode definition with the correct field type

When it happens

Trigger: Thrown at core/chaincode/lifecycle/serializer.go:426 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of hyperledger/fabric@2736b63f8f (2026-09-04). Data as JSON: /api/errors/5843e403d3506788. Report an issue: GitHub.