deepset-ai/haystack · error · DeserializationError

Value ' ' is not a valid member of Enum

Error message

Value '{payload}' is not a valid member of Enum '{value_type}'

What it means

Haystack raised DeserializationError because a payload string was looked up as an Enum member name via cls[payload] and no member with that name exists. The enum value stored in the serialized data does not correspond to any member of the enum class being restored.

Solutions

1. Check the enum class for the exact member name and correct the serialized value
2. If the enum was renamed, migrate old serialized pipelines to the new member name
3. Store the member name (cls[key].name), not the value, when serializing custom enums
4. Regenerate the pipeline serialization with the installed library version

Example fix

// before
{"retriever_type": "DENSE"}   # no such member
// after
{"retriever_type": "dense"}   # matches Enum member name

import enum

def validate_enum_member(enum_cls, name: str) -> bool:
    return isinstance(name, str) and name in enum_cls.__members__

def is_enum_member_name(enum_cls, value) -> bool:
    return isinstance(value, str) and value in enum_cls.__members__

try:
    pipeline = Pipeline.loads(yaml_str)
except DeserializationError as e:
    logger.error("bad enum member in serialized data: %s", e)
    raise

When it happens

Trigger: Restoring a pipeline/component whose serialized init parameter is an Enum, where the payload string (e.g. "OLD_MEMBER") is not a member name of the current enum class.

Common situations: Enum member renamed or removed in a newer library version; hand-edited YAML/JSON with a typo in the member name; payload stores the enum's value instead of its name.

Related errors

• Could not apply arguments
• Could not deserialize type
• Could not find attribute
• Could not import ' ' as a module or callable.
• Could not import

AI-assisted analysis of deepset-ai/haystack@e318778c9b (2026-08-30). Data as JSON: /api/errors/2816beace59cb9c3. Report an issue: GitHub.

Appendix: source

Thrown at haystack/utils/base_serialization.py:328

    # try from_dict (e.g. Haystack dataclasses and Components)
    if hasattr(cls, "from_dict") and callable(cls.from_dict):
        return cls.from_dict(payload)

    # handle pydantic models
    if issubclass(cls, pydantic.BaseModel):
        try:
            return cls.model_validate(payload)
        except Exception as e:
            raise DeserializationError(
                f"Failed to deserialize data '{payload}' into Pydantic model '{value_type}'"
            ) from e

    # handle enum types
    if issubclass(cls, Enum):
        try:
            return cls[payload]
        except Exception as e:
            raise DeserializationError(f"Value '{payload}' is not a valid member of Enum '{value_type}'") from e

    # fallback: set attributes on a blank instance
    deserialized_payload = {k: _deserialize_value(v) for k, v in payload.items()}
    instance = cls.__new__(cls)
    for attr_name, attr_value in deserialized_payload.items():
        setattr(instance, attr_name, attr_value)
    return instance

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