chroma-core/chroma · error · NotImplementedError

Attached functions are only supported when connecting to a C

Error message

Attached functions are only supported when connecting to a Chroma server via HttpClient. The Segment API (embedded mode) does not support attached function operations.

What it means

Chroma's attached-functions feature (server-side functions that derive an output collection from an input collection) exists only on a Chroma server reached via HttpClient. The embedded SegmentAPI overrides attach_function to raise NotImplementedError with a message explicitly redirecting to HttpClient — there is no function engine in embedded mode.

Source

Thrown at chromadb/api/segment.py:1073

        return self._settings

    @override
    def get_max_batch_size(self) -> int:
        return self._producer.max_batch_size

    @override
    def attach_function(
        self,
        function_id: str,
        name: str,
        input_collection_id: UUID,
        output_collection: str,
        params: Optional[Dict[str, Any]] = None,
        tenant: str = DEFAULT_TENANT,
        database: str = DEFAULT_DATABASE,
    ) -> Tuple["AttachedFunction", bool]:
        """Attached functions are not supported in the Segment API (local embedded mode)."""
        raise NotImplementedError(
            "Attached functions are only supported when connecting to a Chroma server via HttpClient. "
            "The Segment API (embedded mode) does not support attached function operations."
        )

    @override
    def get_attached_function(
        self,
        name: str,
        input_collection_id: UUID,
        tenant: str = DEFAULT_TENANT,
        database: str = DEFAULT_DATABASE,
    ) -> "AttachedFunction":
        """Attached functions are not supported in the Segment API (local embedded mode)."""
        raise NotImplementedError(
            "Attached functions are only supported when connecting to a Chroma server via HttpClient. "
            "The Segment API (embedded mode) does not support attached function operations."
        )

View on GitHub (pinned to aecdd12c8a)

Solutions

Run a Chroma server and connect with chromadb.HttpClient, then attach functions there
Feature-detect: wrap attach_function in try/except NotImplementedError and disable the functions path when embedded
Branch on settings.chroma_api_impl before touching the function APIs

Example fix

// before
coll.attach_function(function_id='builtin:chunking', name='chunks', ...)  # NotImplementedError

// after
client = chromadb.HttpClient(host='localhost', port=8000)
coll = client.get_collection('docs')
coll.attach_function(function_id='builtin:chunking', name='chunks', ...)

Defensive patterns

Strategy: validation

Validate before calling

import chromadb

def is_server_client(client: chromadb.ClientAPI) -> bool:
    return 'http' in (client.get_settings().chroma_api_impl or '').lower()

def attach_function_safe(coll, **kwargs):
    if not is_server_client(coll._client):
        raise NotImplementedError('attached functions require a Chroma server')
    return coll.attach_function(**kwargs)

Try / catch

try:
    attached = coll.attach_function(function_id=fn_id, name=name,
                                    input_collection_id=coll.id,
                                    output_collection=out_name)
except NotImplementedError:
    attached = None  # embedded mode: functions unsupported

Prevention

Gate all attached-function calls behind an is-server check
Start function development against a Docker Chroma server from the beginning
Keep a feature matrix of embedded vs server capabilities in your project docs

When it happens

Trigger: collection.attach_function(function_id=..., name=..., input_collection_id=..., output_collection=..., params=...) on an embedded client (chromadb.Client, EphemeralClient, PersistentClient).

Common situations: Prototyping the attached-functions feature locally in a notebook with PersistentClient; running server-oriented integration tests against an embedded client; SDK/wrapper code that manages attached functions regardless of backend.

Related errors

AI-assisted analysis of chroma-core/chroma@aecdd12c8a (2026-08-16). Data as JSON: /api/errors/d9982a87ffe0b6ca. Report an issue: GitHub.