chroma-core/chroma · error · ValueError

Trying to instantiate configuration of type {cls.__name__} f

Error message

Trying to instantiate configuration of type {cls.__name__} from JSON with type {json_map['_type']}

What it means

ConfigurationInternal.from_json (chromadb/api/configuration.py:208) raises this ValueError when the "_type" discriminator in the JSON map does not equal the class you are deserializing into. to_json stamps every serialized configuration with _type = its class name, and from_json enforces an exact match (cls.__name__ != json_map["_type"]), so loading a map of one configuration class through another class is rejected instead of silently misinterpreting fields.

Source

Thrown at chromadb/api/configuration.py:208

    @override
    def to_json(self) -> Dict[str, Any]:
        """Returns the JSON compatible dictionary representation of the configuration."""
        json_dict = {
            name: parameter.value.to_json()
            if isinstance(parameter.value, ConfigurationInternal)
            else parameter.value
            for name, parameter in self.parameter_map.items()
        }
        # What kind of configuration is this?
        json_dict["_type"] = self.__class__.__name__
        return json_dict

    @classmethod
    @override
    def from_json(cls, json_map: Dict[str, Any]) -> Self:
        """Returns a configuration from the given JSON string."""
        if cls.__name__ != json_map.get("_type", None):
            raise ValueError(
                f"Trying to instantiate configuration of type {cls.__name__} from JSON with type {json_map['_type']}"
            )
        parameters = []
        for name, value in json_map.items():
            # Type value is only for storage
            if name == "_type":
                continue
            parameters.append(ConfigurationParameter(name=name, value=value))
        return cls(parameters=parameters)


class HNSWConfigurationInternal(ConfigurationInternal):
    """Internal representation of the HNSW configuration.
    Used for validation, defaults, serialization and deserialization."""

    definitions = {
        "space": ConfigurationDefinition(
            name="space",

View on GitHub (pinned to aecdd12c8a)

Solutions

1. Dispatch on the discriminator: look up the class by json_map["_type"] (e.g. via the module's ConfigurationInternal subclasses) and call its from_json
2. Or call the exact matching class: HNSWConfigurationInternal.from_json(map_with_matching_type)
3. Regenerate stored JSON with the current version via to_json so _type matches

Example fix

# before
cfg = HNSWConfigurationInternal.from_json({"_type": "OtherConfiguration", ...})
# after
m = json.loads(raw)
cls = {c.__name__: c for c in ConfigurationInternal.__subclasses__()}[m["_type"]]
cfg = cls.from_json(m)

def from_json_typed(cls, json_map):
    actual = json_map.get("_type")
    if actual != cls.__name__:
        raise ValueError(
            f"_type {actual!r} does not match {cls.__name__}; dispatch on _type instead"
        )
    return cls.from_json(json_map)

def from_json_dispatch(json_map):
    import chromadb.api.configuration as m
    target = getattr(m, json_map["_type"], None)
    if target is None:
        raise ValueError(f"unknown configuration type {json_map['_type']!r}")
    return target.from_json(json_map)

When it happens

Trigger: HNSWConfigurationInternal.from_json({"_type": "SomeOtherConfigurationInternal", ...}); a _type value with different casing; loading nested configuration JSON with the outer class's from_json instead of the nested class; version skew where the producer class was renamed.

Common situations: Generic loading code that picks a fixed class regardless of _type; copy-pasting deserialization calls between configuration types; renamed configuration classes across chromadb versions invalidating stored JSON.

Related errors

• Invalid configuration type: {parameter.value}
• Invalid parameter name: {parameter.name}
• Invalid parameter value: {parameter.value}
• Invalid parameter name: {name} for configuration {self.__cla
• Invalid parameter name: {name}

AI-assisted analysis of chroma-core/chroma@aecdd12c8a (2026-08-16). Data as JSON: /api/errors/6c1ac55df54b32a0. Report an issue: GitHub.